Here is what I know.
The T3550, TKO500 and TKO600 are all 5-speed transmissions that have 3 shifter locations. The difference between Ford Installations and GM installations is the drilling of the thicker lower mounting ears and the input bearing cover outer pilot dimension. The GM installations uses the Ford output spline count and must have a different front driveshaft yoke.
The T56 is a 6 speed not related to the T5 in any way and comes in one OEM flavor with the the front half of the bell housing specific to the engines that it is mated up to. There is a T56 Retro that is rare, expensive, and meant to bolt up to the T5 flywheel housing. The early T56's are prone to have the 3/4 shift fork fail. The shift forks are powdered metal and crack, leaving you in two gears simultaneously. There are billet forks available to fix this problem. It is a known common problem.
The T5 is a trans that Tremec acquired from Borg Warner. The T4/T5 trans that has been used in everything from a 4 cylinder camaro, V8 camaro, S-10, Isuzu trucks, Astro Vans, Ford Mustangs, Thunder birds, Jeeps, etc.
The T5 and T4 share many interchangeable parts. The T4 is a T5 with no overdrive gear and a rear housing that will not allow you to add it. the difference between the T5 for Fords and the T5 for GM is the lower mounting ears and the input bearing cover pilot size as well as output spline count. The strongest T5 from the factory is the V8 Camaro transmission capable of 300lb-ft, followed by the V8 mustang transmission (limited only by the input splines. The weakest is the Jeep followed by the S-10. The V8 camaro and the Astro version are the only T-5's with 1-5/32" 26 input splines. The Astro van version however has the weaker 1st gear. The 4 cylinder and 6 cylinder camaro as well as all the S-10 have the 1" 14 spline input shafts. The Ford has the Ford 10 spline as well as the Jeep. 4 x 4 versions are simply the standard T5 with an adapter and T-case bolted on to it. So if you want to build an AWD or 4WD you can by simply playing mr potato head.
Now on to other good things. The Camaro T-5's have longer splines than the S-10's. The Camaro T-5's have shorter input bearing covers. The V8 camaro T5 has the much desired short pilot on the input shaft vs the 4 cylinder and 6 cylinder transmissions because of pilot pushing depth. The Ford T5 uses a larger pilot bushing diameter. The Camaro transmissions are twisted 18 degrees and have the rear mount done this way to bring the shifter 2" closer to the driver. The bellhousing and the tail shaft have the mounting rotated. Most GM flywheel housing castings have both patterns, however only one drilled. I own a rare 2 year production Pontiac only V6 flywheel housing that has both starter humps and both patterns drilled. This was popular with midget racers that were running the 2.8 because they could use either the FWD or RWD engine. The S-10, Jeep, and Ford units are mounted straight up. The Astro Van transmission uses the straight up S-10 tail section with an adapter housing that moves the shifter over 7" towards the driver.
The rear housings are interchangeable with the front housings, however the speedometer gear moves a little bit (covered on inliners). So building a Hybrid is done with a V8 Camaro T5 and the top cover and rear tail section of the S-10 T5. this gives you the strength of the V8 front section and moves the shifter forward as well as mounting the transmission straight up without having to cut input shaft splines, trim off the pilot, or cut the front bearing retainer. The downside is that folks thing the V8 camaro transmission is gold with prices everywhere from $200 to $800.
For more information right from the source, visit the factory web site
http://www.ttcautomotive.com/English/products/T-5.asp#Car
