This is a post from another site.

Do you have a Gen I or Gen III/IV engine?

If Gen I, you can use a stock LT1 T56, flywheel, and hydraulics with no issue as long as you have a 1 pc RMS engine. The 2 pc RMS engines require a $400ish conversion flywheel. The 93 T56's had slightly shorter gears all around and were rated for less torque. Generally the concensus is to avoid them.

If Gen III/IV, the LS1 F-body T56 is the ticket. All 94-02 F-body T56's had the same gear ratios as far as I am aware.

You can convert a 98-02 F-body T56 to work with a Gen I engine but it requires an adapter plate at least, maybe other issues too. A 94-97 T56 costs around $600-$1000 for parts to convert it for use with a Gen III/IV engine down the road. That may affect your decision.

The LT1 T56 uses a strange clutch with a reverse-pointed slave cylinder. They're fairly unique and there arent many clutch options out there. There are enough, but aside from maybe the high end Mcleods, they all use the exact same Valeo pressure plates. They increase grip by changing the clutch disc material, not by increasing clamping force. Normally this isnt a big deal, but its a transmission they only made for 5 years, you're just not gonna have a TON of options on it. But there is enough available that it isnt a huge concern. the clutches do cost a little more though it seems. $250 is about the starting point.

The LS1 T56's seemed to have crappy hydraulics from the factory. I think i read that GM didnt allow full pressure to the slave cylinder, so you never got complete clutch disengagement... something weird like that? Hence things like the "drill mod". LS1 T56's seem to go through synchros a lot faster, but that could be because of crappy hydraulics or because LS1's make oodles and caboodles of power. Nothing a fancy aftermarket $300 Tick master cylinder cant fix. The LT1 T56's despite being older and more worn out seem to last just as long, but they are getting very old now.

CTS-V and GTO T56's can work, but they require a lot of conversions to get them into other vehicles. The F-body ones are a direct drop in. If this is for a non F-body, then it may not matter so much. Corvette T56's are integrated into the rear axle and IRS, so they pretty much only work in corvettes.

I have a T56 from a 94 TA that was bracket raced and power shifted hard. I learned how to drive a stick with it in my car, and the thing makes noises, but it's held up great over the years Ive had it. They're very tough transmissions, and I think everything from 94+ had at least a 450 ft lb rating.