Upgrade From3,5V8 4sp to 3.9V8 5sp

I've got a 1987 110 Pickup with 3.5 V8 motor and LT95 4sp gearbox. My question if I want to upgrade to a 3.9 V8 with 5sp gearbox out of a 1990's Discovery will I get a combo were I dint have to modify any engine or gearbox mountings for the new fit and up till what year on the Discovery will work. Thanks