I do not understand what everyone likes about hydraulic clutch linkages?
First let me start by saying whatever system an individual is running, if it works well, fits in their budget and most importantly they are happy with it than thatís the system they should be running. So if youíre happy with the z-bar then fantastic. With that said I can give some insite as to why hydraulic, which is IMHO superior weather itís my kit or someone elseís.
too close to header will heat the clutch fluid to vapor point, no clutch.
You hit the nail on the head issues with a hydraulic clutch are usually the result of an improper instillation. Hydraulics have been used for breaking for about 100 years and there is a reason brake lines are all routed away from heat sources. If the hydraulic lines are properly run this will never be an issue.
use the stock Mustang parts and you know it is going to work.
while that is true it may or may not be best given the application. IF you are NOT running a T5 and you have OEM equipment than yes the z-bar is the easiest and probably most effective way to go however it does have two drawbacks. The first is a mechanical pivot that wares with time. As long as you keep it maintained and replace the bushings as they begin to become loose it will function well but a lot of people let the bushings go to long and that can reduce the smooth action of the linkage, which causes clutch chatter. The second issue is the z-bar pivots on the engine block or bellhousing (depending on the setup) and in high torque applications as you are clutching the engine can rock, again eliminating the smooth action of the z-bar, resulting in clutch chatter. Even with those two issues there is little to no reason, IMHO, to ditch the z-bar in a 4-speed application especially if you upgrade it with heim joints and such.
With all that said going to a T5 you are no longer using stock parts and stock parts are no longer the BEST option. Its more complicated and using the OEM clutch linkage is not always going to give you the best result. There are three main ways to install a T5 in a classic Mustang while maintaining the z-bar: OEM 4-speed bellhousing with T5 adapter, T5 bellhousing with old school clutch fork and pivot block, or Aftermarket bellhousing such as a Quicktime.
If you go with the OEM bellhousing and adapter plate this is probably the best way to maintain the z-bar, have good clutch action, and keep costs to a minimum, however it has one major flaw. The issue is early Ford transmissions had much lower tolerances in relation to the input shaft, upwards of .015". This meant the bellhousings could be out of alignment by as much as .015 with no issues. The T5 on the other hand has an input shaft tolerance of .005" so if your old school bellhousing is off by more than .005" (some are some arenít) not to mention any tolerance issues with the adapter, you will have premature failure of the inputs shaft bearing and or the pilot bearing (most common the pilot bearing) This can be fixed by using a dial indicator to take measurements and shimming the T5 adaptor but most installers don't do this step.
The second solution is to retrofit a T5 bell with an old school clutch fork. I do not personally like this option as they are way less smooth as a hydraulic clutch and not even as smooth as an OEM 4-speed setup IMHO.
The third option of an aftermarket bellhousing designed specifically to work on a T5 AND use the stock linkage is probably functional the best but big $$ so it just depends on your budget.
Because of the drawbacks to all three of these options most people go with either a hydraulic clutch or a cable clutch.
As I said before "hydraulic... is IMHO superior weather its my kit or someone elseís." There is a reason brakes went from mechanical to hydraulic. Once a hydraulic system is set up and working properly they are relatively maintenance free and the action is smooth. I would even go so far as to say a properly set up hydraulic clutch is not only lighter pedal effort and smoother action than the z-bar but you also get better clutch feel translated through the system (the change in pressure you feel against your foot as the clutch goes from engaged to disengaged)
Most of the problems people have with a hydraulic clutch happen in getting it set up correctly, and few happen after the fact due to an issue in the way it was set up, but a correctly set up system should function flawlessly with fantastic longevity just as brakes do. I have had a hydraulic clutch on my Galaxie for over 8 years and in my Mustang for more than 10, without issue.
Most anyone makes headers to clear the stock linkage.
Again a true statement but no all headers will clear the z-bar and the headers that don't clear become an option with a cable or hydraulic clutch. This is even more important if the car is not running OEM steering. If the car has been upgraded to rack and pinion or even a Bourgson type box than having more header options is a good thing. Basically the further you move fro stock the less likely stock options are to function the best/simplest.
Push the easy button!
While that may be the easiest and best option for your car it does not mean that that is a true statement for someone elseís car.
Again this is my opinion, but it is substantiated with a lot of experience and Mustang knowledge and the bottom line is as long as a person is happy with the way there car performs than that IS the correct setup for them regardless of which one they go with.