Iím doing an engine/trans swap on an 87 Ram 50 (2WD). My truck has a 3.90 open rear end.

Will the third member from an 85 or 86 2WD interchange with the differential on my 87? If the differential will not interchange will the whole rear end bolt in? Is there any differences in the bolt pattern for the pinion yoke between the manual and automatic differentials ( I know they list different U Joints).

The reason I ask is that after I get the truck on the road I may end up wanting to go to change over to 3.55s and was just wondering how much work Iím in for.