The axles will fit and the are 3/4" wider on each side. If you want disc brakes on the rear, it probably would be easier and cheaper to find a Turbo Coupe rear end. Auto Turbo Copes came with 3.73's and Manual TC's came with 3.55's. The rear end goes for $150-$300 depending on your area and your luck. The rear disc calipers are about $170 each for rebuilt units with pads, brackets and hardware. Of that $170, about $85 is for the core charge. I don’t recommend running the junkyard units since they tend to rust up and not work properly. Add to that the cost of the caliper support brackets that you will have to buy, because the TC caliper brackets are welded to the rear axle housing.
Here's my experience with the Turbo Coupe rear end swap...
It takes 2 guys the first day to get the old rear end out and the new one bolted in place. It takes 1 guy another whole day to do the brakes.
Auto trans Turbo Coupes come with 3.73 gears and manual Turbo Coupes come with 3.55 gears. I choose 3.55 since I do more highway driving.
You will need a several sets of fittings, I recommend that you get them from Matt90GT's website,
http://www.svo73mm.cjb.net/. Read Matt's instructions thoroughly, everything you need to know about the brakes is all there. You need to be patient and follow all the internal links, and there are many of them. You will need 2 fittings in the rear to adapt your old brake tubing to the TC disk brakes. The fittings go between the steel tube and the caliper
brake hose. You will need another set of fittings to make a 2 port to 3 port adapter. To make life simpler, just buy the kits from Matt. You could piece them together, but it's not worth the time unless you work at an auto parts store with all the fittings ever made. You will need to drill the quad shock mounting holes 2” below the holes drilled for the Turbo Coupe mounting points. The bolts are metric, so don’t loose them or the nuts. A 15/32” drill should be about the right size unless you have access to metric sized drill bits. Going without quad shocks is not an option unless you have aftermarket parts to soak up the wheel hop.
You will need a proportioning valve, Summit has one for $40 + shipping.
You will need a kit (FMS makes the part) to gut the stock proportioning valve, Summit also has that, about $10.
You will need a new master cylinder, see Matt's site and make you choice. I used a 94-95 Mustang master cylinder. Note that rebuilt 94-95 Mustang master cylinders do not come with a reservoir. That means a trip to the junkyard and some more money spent.
Your brake pedal may be very hard and almost impossible to lock up the brakes. I had to replace the front calipers with 73 mm calipers from a 91 Lincoln Mark 8 to get the braking performance up to par.
Bleeding the brakes will require 2 people and some coordinated effort. I don’t recommend using you wife or girlfriend to pump the pedal – they get offended when you yell at them. I used a homemade power brake bleeder constructed from a garden sprayer and some fittings from Home Depot. It cost about $25 and was worth every penny.
See
http://www.mustangcentral.net/tech/brake.html for help with the emergency brake - the stock setup tends to lock up and not release properly.
All in all I have been very pleased with the results
