Yup, your right about finding a reg cab, Its gonna be a needle in a haystack for sure. As fare as the rearend goes, the non trd 3rd member differances from 4cyl to 6 cyl was the 2 pinon to the 4 pinion and bearing supports to beef em up, I could be wrong?(and probably am)
all of the non-trd rears are exact same as far as pinion count goes.... the only difference is the different gear ratios depending on engine/trans combo.