I just did this swap. You need:
-Stiffler's crossmember for 94-98 GT with t45/3650 (stock crossmember will not fit)
-Dallas Speedcal (converts OSS to VSS)
-3650 Shifter (different from T45)
-79-95 style trans mount. I recommend the OEM rubber one.
-3.2 quarts of pennzoil synchromesh
I did the swap mainly because you can get a brand new 3650 directly to your door with all the TSBs done for $1060 from ebay. I would NOT recommend buying a used one.
Install is the same as for the T-45 except you have to unhook the air intake from the motor and put a jack on the front of the oil pan and jack it ALL the way up until the back of the motor touches the firewall. If you don't do this, the 3650 will not clear going in as it is a little fatter than the T-45.