Even if the two trannies are different models, you can swap one for the other. Not a direct bolt-on in all cases, but doable. First thing is to I.D. both models. There is a code on the driver's-side door jamb, or you can look at the pan on the bottom. If either model has overdrive, it will be the AOD.
No overdrive is a C-6, the code is "K", and the pan will have a notch in one corner. While you're at it, I.D. the transfer case, too. Some models in the same year had different ones in the mid-80's. They will all bolt up to the various transmissions, but the shifter linkage changed from one to the next. The NP208 has a smooth case, while the Borg-Warner models have a bunch of fins or slots in the case.
Both the 85 and 86 should have a Ford 8.8" rear axle, but the driveshaft may be a different length, depending on the tranny.