Can I use any other tranny in Toyota 4x4??

Im looking for a Transmission for a 1990 Toyota 4x4 Pickup with a 22R Fuel injected engine but, Im haveing problems. This truck has the 5 speed tranny that has both the shifters on the same 6 bolt plate (I think the G series) and the others Im finding has two plates (one for each shifter the W series I think). Can anyone tell me what the differance is and if they will interchange? It looks to me like as long as I get the transfer case and bellhousing with it they will interchange but, I cant tell for certain. Any help here would be great... Also, I was told that the "G" series came out in the carburated trucks and the "W" series is what would have come out in the Fuel injected trucks. If this is right, that would mean my tranny have been changed before and I should go back to the "W" series. Can anyone shine some light on this? PLEASE?? Im haveing a REAL hard time find the "G" tranny.
Thanks for ANY help. It much needed!!!