I dont knwo about mk3 granadas but I do know that you cannot use a 2wd diff with 4x4 shafts.

To use a 2wd diff in a 4x4 beam you need to chop off a mounting lug on the beam and re-weld it 1/2 inch over to accomodate the bigger width of the diff (7 inch versus 7 1/2). You also need to use 2wd shafts, these fit fine into the hubs and arms etc.... so basically to put a 2wd diff into a 4x4 beam you need diff and shafts & a grinder/weld set.

Cheers
Dan