In that generation trans the O/D unit is effectively the tailshaft. The 4wd O/D unit also serves as the transfer case adapter/mount. You can unbolt the 2wd O/D unit from a RE series trans main case and a 4wd RE series O/D unit will bolt on to it. There is a clutch depth measurement that should be taken to make sure the O/D piston applies properly. And be warned that the 2wd front section may not have the same clutch pack counts as a 4wd may have.