I have a 92 Dakota Le 4x4 with the 3.9l and the 42rh trans. Is the only difference between the 4x2 and the 4x4 model the tail shafts or are there more detailed differences? Reason I ask is because I'm interested in getting one from either a 4x2 or 4x4 model (IF I can find one) and rebuilding it to minimize down time of my truck

 

IDk if the 4x4 and 4x2 42RH trans are different but it seems like they would have different designations if they were or the extra parts would be transferable to a replacement trans.
Not that I want to make things more complicated but the 46RH is supposed to fit right up to the 3.9. It is stouter than the 42RH. You can see the diff on the FAQ page. I was thinking I might get one to rebuild and replace the existing 42RH on mine

 

The tailshaft is different and you get to build the transmission up from it, so ...

For checking the part numbers for the housings are 4461066 for the 2WD, and 4661105 for the 4WD 4 speed autos.

*Pulled from the 1990-1993 Parts List, available in the FAQ*

RwP

 

OK will look for a 4x4 to rebuild then.

 

the front half of the trans is identical, the differences for the 2wd vs 4X4 is in the tailshaft itself which unbolts.... for that matter you can get a 46RH and it will bolt right in if you have the converter for the 46.... input (back part that sticks into the trans) is larger on 46 so that won't work from the 42RH ...
dipstick and tube, front inspection plate are only other differences... 46 is exactly same length as the 42/44rh... no mods to driveshaft.
and... ready for this? The tailshafts with all of the OD stuff will interchange between the lighter and the heavier trans.... same part!!! Ive done "a few" of these trannies and swaps between different trucks/vans. .