8 1/4 durability????????????????

I'm not big at cross-breeding either, but I've seen metion of the 8.8 Ford out of a Ranger a couple of times. Asked a Blue Oval buddy, and he looked at me kinda strange. His comment was the axels are offset, and thought this was not an 8.8. He asked why the 8.8 out of a Mustang wouldn't be a better avenue? They have posi's tons of after-market stuff, and aren't hard to come by. 5 lug axles being one of them. So...what are the reasons these aren't considered?
Mac