Rear leaf springs- drop? Bushings?
I have my 1970 Mustang coupe apart to do a bunch of work. One of the things I'm doing is replacing the rear leaf springs. My old ones seem original and are sagging badly.
I'll probably replace them with Eatons.
Ride quality is important to me, but it doesn't need to be soft and "floaty". Firm is fine as long as it takes the edge off of road imperfections/doesn't shake the car apart. Handling is important too, I like to go for spirited drives on back roads and occasionally autocross. Track use in the future is a possibility, though this is primarily a daily driver and road trip car.
With all this in mind, I'm leaning towards Eaton ML759, Eaton "Improved Handling" 138lb. rear leaf springs, but I can't decide how much of a drop to get. My original springs have sagged so I don't have any reference of what stock height is supposed to look like. I'm doing the 1" Shelby drop in the front, which should lower the front by about 1/2". I also still have the original front coil springs and was planning to keep them but put in a bigger front sway bar.
So how big of a drop should I get for the rear leaf springs? I think I want to go as low as I reasonably can without running into ground clearance issues. I don't want to start hitting my long-tube headers on the ground, I need to get over speed bumps, and I don't want to start having tire rubbing issues (but with 225/50R16 all around that probably won't happen).
I also need help deciding what bushings to go with. Like I said I don't want a harsh ride, but firm is ok. I've heard that lower friction in the bushings will improve the handling, are urethane bushings good for that?