I've twisted 2 sets of Moser 31 spline axles in the same manner as your stock one here. 3200 lb stick shift 393w small block 68 Fastback street car 11.48 @119.5. Put the 33s and a spool in it as the Moser warranty doesn't apply to 28 and 31 spline axles. I then pulled the 33s out to fix an axle bearing a few years ago and the 33 was twisted too. Called Moser for warranty and they said they wont replace it until its twisted a full spline. I tried to explain to them that this was a stick car and if it gets that bad it'll just snap but they wouldn't hear it. So I dont buy Mosers anymore. Strange is the way to go. Moser cuts their splines after hardening. You can see it when you get them. Strange cuts splines and then hardens, much better axle for like 20 dollars more.

Swapping to later model 68 and up Ford brakes will require changing spindles and will create some really bad bump steer issues on 64.5-66 mustang's due to the placement of the steering arms on them. Wilwood makes a 12.3(?) Inch 4 piston rotor front brake kit and also a rear kit that will fit with 15 inch wheels. I'm not sure it will fit with all of them but most. Mustangsteve.com sells a really cool Fox body booster kit that fits early Mustangs, which I like because if you have a failure you're not searching for an aftermarket part, you can get a new booster from the parts store.

Once you've taken care of the brakes I'd look at upgrading to a Borgeson power steering box, huge upgrade over the factory control valve/ram junk. Then start doing front suspension mods to make the thing actually handle. It's real fun to transform these old cars for people and make them stop, handle, steer and drive unlike any old Mustang they've ever driven. I can also not stress enough the importance of a good alignment with modern numbers. The factory specs are the worst. What made you chose 16 inch wheels? Pretty limited tire size choices there.

Ok, I'll keep you in mind but I was hoping to find someone with a broken set 2-3 pistons that they'd be willing to sell. As a last resort I'll pick up this set from you.

Cringe away buddy, I'm still gonna keep doing it. I like shifting it like a motorcycle on the street, put tension on the lever and blip off the gas a little. Boop, next gear. Just had it apart last month for an inspection and it looked perfect inside aside from the brass pads on the shift forks that replace the nylon ones Tremec thought were necessary to reduce NVH. I wish someone made some shift forks for the TKO that were like a toploader fork, no pads to wear out. Stupid design.