The GGSX transmission and x-fer case are NOT compatible with the 1G rear differential. If you put a 1G transmission and x-fer case in you will need a 1G rear diff. All 1G rear differentials use the same ratio provided that they all came from a turbo 5-speed (the automatic is different). As for what year transmission to use, it won't matter as long as the transmission and x-fer case come from the same era (i.e. both 22-spline or both 23-spline).
So, in short, you CAN swap a 90 DSM transmission AND x-fer case (but it'll have to be BOTH, not just one or the other) and you will need a 1G rear diff too (92 GSX is fine). You should, however, be careful with the shifter assembly bracket on the transmission as they're not all the same. I believe that '90 and earlier are different than '91 and later so do some research on that.