I have a SSBC adjustable prop valve sitting in there waiting for me.. $45 from Napa with a discount. Not sure what it would normally cost, but I imagine a lot cheaper than some 'specialty' stores.. Although, maybe not in the US.
In rank of Ford rear end strength (in stock form), you have the 8-inch, then the 8.8", then the 9-inch.
8-inch rears in the correct width and setup for a leaf spring passenger car --such as a Mustang, is not too terribly difficult to find that will simply bolt-in. Bolt-in 9-inch rears, on the other hand, are not so easily found in the wrecking yards anymore.
The 9-inch rears ceased production in the Ford cars in 1980, and in the Ford trucks in 1986, so (wrecking yard) availablity has been drying up for a long time now. --Add to that the fact that everyday, wrecking yards all over the U.S. are crushing good cores, and that just speeds up the demise of what little is left out there.
It's eventually going to come to a point (outside of buying a custom fabricated aftermarket 9-inch), that coming across a wrecking yard, Ford-produced, 9-inch for a swap into your old Mustang will be virtually non-existent (even more so than what it is now).
Realizing this, I decided to buy a '96 Explorer 8.8" rear yesterday to see what's needed to put it under an early Mustang (my '68). It didn't have a Traction-Lok differential [ ] --but, that can be installed later. This '96 Explorer 8.8" did come standard with 31-spline axles, disc brakes and 3.55 gears, heavy-duty 3ΒΌ" diameter axle tubes and large axle bearings --rear end capacity rated at 3200 lbs, compared to 2750 lbs for Ford Ranger 8.8" rear.
...it also has an ABS sensor (2-wire connection) in the top, center, of the housing that could possibly be used with an adapted stand alone ABS unit at some future date...hmmmm
It's eventually going to come to a point (outside of buying a custom fabricated aftermarket 9-inch), that coming across a wrecking yard, Ford-produced, 9-inch for a swap into your old Mustang will be virtually non-existent (even more so than what it is now).
It's already at that point where I live. None of the salvage yards have anything much older than 15 years so finding a factory 9" rear there is not going to happen, however the popularity of 9" has maintained a steady stream of aftermarket support and bolt in Mustang housings aren't too hard to find thru other sources like Craigslist, ebay, swap meets, even the parts section of the auto trader occasionally has them, not to mention the classified ads on devoted classic car sites like VMF.
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"It's not having what you want, it's wanting what you've got!" - Sheryl Crow
It's eventually going to come to a point (outside of buying a custom fabricated aftermarket 9-inch), that coming across a wrecking yard, Ford-produced, 9-inch for a swap into your old Mustang will be virtually non-existent (even more so than what it is now).
It's already at that point where I live. None of the salvage yards have anything much older than 15 years so finding a factory 9" rear there is not going to happen, however the popularity of 9" has maintained a steady stream of aftermarket support and bolt in Mustang housings aren't too hard to find thru other sources like Craigslist, ebay, swap meets, even the parts section of the auto trader occasionally has them, not to mention the classified ads on devoted classic car sites like VMF.
This is true, but now you are relying on individuals to source the 9-inch rear ends from, and no one can say how long that will last. With fewer and fewer 9-inch rears available, people will buy them up for their own use when available and affordable, then there will be even less available for the rest of those looking, just for the simple fact that the pool of availability is drastically evaporating at a rapid rate whether the supply is reliant on the wrecking yards or whether it's from individuals.
I had inquired earlier this week about a 9-inch for a '67 Mustang I'm working on for a customer. They wanted $350.00 just for the housing and axles --that's with no brakes and no 3rd member! That's $50.00 more than I have ever paid for a [complete] 9-inch assembly.
I'm a very strong proponent of the Ford 9-inch, but the availability and economics of trying to procure one anymore is quickly getting to not be worth it compared to the 8.8", especially compared to what some of the 8.8" versions have to offer, i.e., many come standard with 31-spline axles, disc brakes, the high availability of Traction-Loks and many with really good [performance] ratios.
Even if you find a passenger car 9-inch that will basically bolt-in, [short of getting a Boss 302/Cobra Jet 9-inch] it isn't going to have 31-spline axles, and very few are going to have a Traction-Lok differential, and most pasenger car 9-inch rears will have very anemic gear ratios. These are all additional costs you will have to incur to beef the 9-inch up beyond the initial purchase price of the core housing assembly to have the same features as the components that often are standard on the 8.8" --which unlike the 9-inch, (anymore), the 8.8" is generally very affordable and very abundant.
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My current Mustangs:
1968 Mustang notchback
1990 Mustang GT
2003 Mach 1
Producer of Mk VII and SN-95 Rear Disc Brake Conversion Brackets Since 2002.
http://www.ultrastang.com
I started out with nothing, and I still have most of it left.
Ultrastang, I am anxious to see to see your findings. I have a lot of respect for your expertise in this area. Some info posted by people, myself included, can be misleading at times. I don't think it is because of bad intent, but that we are learning as we go. Maybe a fresh thread would be good so people searching will not have to read through so many post to get to the good info on Explorer swaps. When I get my engine a little more sorted I plan on swapping to 31 spline 9" ends and axle in my 95 Mustang 8.8 under my 67. If you get a chance, compare splines on the 9" 31 spline vs 8.8" 31 spline axle. I have heard in other threads they are the same.
Ultrastang, I am anxious to see to see your findings. I have a lot of respect for your expertise in this area. Some info posted by people, myself included, can be misleading at times. I don't think it is because of bad intent, but that we are learning as we go. Maybe a fresh thread would be good so people searching will not have to read through so many post to get to the good info on Explorer swaps. When I get my engine a little more sorted I plan on swapping to 31 spline 9" ends and axle in my 95 Mustang 8.8 under my 67. If you get a chance, compare splines on the 9" 31 spline vs 8.8" 31 spline axle. I have heard in other threads they are the same.
Thanks Brian. While I do have a vast amount of knowledge about the Ford 8- [and particularly] the 9-inch rear ends, I don't know everything there is to know about them.
In the last 15 or so years, I've read all the literature I could get my hands on about the Ford 9-inch rears. I've also spent a lot of time (literally) crawling around under countless Ford cars and trucks looking for Ford 9-inch rears and Traction-Lok 3rd members and noting the differences in what I saw while I was there.
I've handled, built, and installed plenty of Ford 8- & 9-inch rears, but I have never installed an 8.8" into an early Mustang, so this is new territory for me. I have been "studying up" on them though.
The 28-spline count and diameter of the early Mustang axles is the same as on the 8.8" axles. However, there is a (for the lack of a better term) "button" on the end of the 8.8" alxes for the C-clip retainers. The axles are not interchangeable from one housing type to the other.
__________________
My current Mustangs:
1968 Mustang notchback
1990 Mustang GT
2003 Mach 1
Producer of Mk VII and SN-95 Rear Disc Brake Conversion Brackets Since 2002.
http://www.ultrastang.com
I started out with nothing, and I still have most of it left.
I have a truck trac-loc from an 8.8 that should work with 9" axles of the right length (custom) and housing ends with correct bolt pattern for my SN95 brakes. Moser and a couple other companies make housing ends to convert an 8.8 to 9" style axles. The Moser part# is 7700 and sell for $84.
The problem is there are no 8.8" swaps that are "Direct Bolt Ins"
The Explorer versions are still a hack job.....
You can buy "New" direct fit 9" housings on Ebay for $295 or so. I can't see the bargain in an 8.8 swap just yet.
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] --but, that can be installed later. This '96 Explorer 8.8" did come standard with 31-spline axles, disc brakes and 3.55 gears, heavy-duty 3ΒΌ" diameter axle tubes and large axle bearings --rear end capacity rated at 3200 lbs, compared to 2750 lbs for Ford Ranger 8.8" rear. 
