Quoting raptorreed:
Only Autos are different. DSM and USDM GVR4s share the same ratios. If you have a 22 spline trans, then you would need one from a '90 DSM or you just get a 23 spline tcase and trans from 91-94 DSM.
I had a 3 bolt LSD rear diff from a DSM in my VR4. You might get your ratio information mixed up with the GGSX stuff.
It's incredibly easy to swap the output shaft.. a few bolts and a circlip.
I think i have about a dozen spare output shafts kicking around, in case anyone ever needs one.