the TCU changed between the 1996 and 1997 model years. The input/output shafts may be different spline counts around 91-92 but I forget - someone who knows more than me will probably show up and answer that one definitively. Also 2wd vs 4wd ones are different because of the tailshaft housing, you can change them over but it's easier to just get the right one in the first place. Other than that I think they're at least compatible.
EDIT: also, I think they're compatible across TCU changes (the mechanical portion anyways), pretty sure you just need to use the TCU for your model year, the tranny *should* be the same unless I'm blatantly wrong.