91 stanza tranny problem

I have a 91 stanza xe, the original trans was non-locking, front wheel drive, we got a used one from a yard and they said its the same one but on the side its stamped "4WD". is this the same tranny? there are no #'s on the whole thing except for a serial # I think. We are trying to get the drivers side half-shaft in but it wont go all the way, its suppose to "snap in" but it doesnt and wont stay in there on its own. When we move one wheel clockwise the other turns counter clockwise. J