I had several of each on hand in the shop for years (actually B5 and SC10, as ProSC10's were not even a thought at that point), but now for about the last year I have no complete SC10 gearboxes, and no rear motor B5 boxes, but several of the mid motor variety 5 series still ... several years ago I did some internals testing, and the only thing that was close to 'drop in' with no mods, was the 4 and 5 series diffs were interchangeable (if using the metric outdrive bearing 9826 SC10 gearbox, but not with the earlier 9574 SAE B4/T4 case) , although some of the 4 series gear diffs (SC10) did need a minor modification to work properly with the wider 5 series (ProSC10) idler gear in a 5 series (ProSC10) case... as for trans cases themselves, never even tried swapping, never had a reason to, but definitely would not be 'drop in', with no mods ...

I guess the question before pursuing might be what was your reason/hoping to accomplish to even want to try it, as they each had their strong/weak points in comparison? ...