If using any of the stock wheels - no, either width FMJ differential will interchange. The difference is the rear tires are inwards on the earlier width.
Now if using existing wider aftermarket wheels or wheels of different width than what came on on FMJ's then you might run into interference with either the leaf springs (early diff in later car) or fenderwell lip (later diff in earlier car) due to backspacing difference.
I have heard of using the 8 inch Super Coupe wheels on an later M-body causes problems with fenderwells - but no first hand knowledge of that (just hearsay).
BudW
Edit: IMO the early diffs are way too narrow for the fenderwell. It looks like rear wheels are just too far inwards.
Now if using existing wider aftermarket wheels or wheels of different width than what came on on FMJ's then you might run into interference with either the leaf springs (early diff in later car) or fenderwell lip (later diff in earlier car) due to backspacing difference.
I have heard of using the 8 inch Super Coupe wheels on an later M-body causes problems with fenderwells - but no first hand knowledge of that (just hearsay).
BudW
Edit: IMO the early diffs are way too narrow for the fenderwell. It looks like rear wheels are just too far inwards.