rear ends?
 

IF YOU HAVE TWO 8.8 REARENDS AND ONE IS POSI AND THE OTHER ISNT, AND THE ONE WITH POSI HAS DRUMS AND THE ONE WITHOUT HAS DICS THEN WOULD IT BE EASIER TO CONVERT THE DISC TO THE POSI REAREND OR TO JUST TAKE THE POSI OUT OF THE DRUM ONE AND PUT IT IN THE ONE WITH DISC, KEEP IN MIND THAT THE POSI IS IN A 1990 FORD AND THE DISC ARE ON A 1996 FORD, IS IS POSSIBLE AND WHICH ONE WOULD BE BETTER?

Since your only talking about the differential being different it would be easier to swap the traction lock diff into the newer disk rear end. The only difference between the two, other than the brakes and differential is the length of the axles which will not matter for the differential to work. However keep in mind that the width of the rear end itself is going to be different between the two and that should be a factor when you consider what the rear is going in to.

Bill