If the heads are 243's and are stock on a 6.0L engine, you are looking at an LS2. The 243's also came on LS6 engines, but are 5.7L engines.
As for the 94 T-56, it will not work behind the LS motor. There are a bunch of differences besides just the bell housing. The clutch release (throw out bearing) is completely different (push instead of pull). I believe the input shaft is different as well. You need to find a T-56 out of an LS car (Camaro or GTO) for it to mate correctly.