Bought a 96 GT with an incomplete 3SGTE swap and am having trouble determining the generation. Best way/place to find that information?

Read the VIN from the block and figure out what car it came from.
Short of that, look for various posts describing the differences b/w the different generations and figure it out. Could be mix of different components though, as some parts interchanged and/or were upgrades from one gen to the next.