measure the distance between where the backing plates mount on your diff flanges and the 8.8 from the explorer.
if there is not any difference you are good to go, if there is a difference you may be able to offset the difference with different wheels from different mustangs, 94-98, 99-2004. 2005 & up. the 2005 & up mustangs have the offset of the wheels toward the inside. there is a difference between v-6 & v-8 in width hieghts etc, this works out in your favor id the diff is a little wider.
dont forget the exporer axles have different bolt pattern which is 4.5 inch on a 5 lug pattern.
also the parking brake cables on your fairmont will need altering for the disc brakes, a little pain in the backsiide but can be overcome.
you will have to alter the brake lines as well to match the fairmont, no big thing.
choose carefully, a lot of exploders have posi rear ends.
i think the driveshaft mounting flanges are the same pattern, if not you may be able to swap them out, keep the drive shaft bols from the exploder, as they will come in handy.
im pretty sure your drive shaft will fit the 8.8 with out modification.
check the gear ratios as well, for instance, if you are running a c4 trans, and 3.73 gears, it will take off like a rocket, and fall flat at around 60mph.
other things you may want to consider is booster/master cyl set-up, proportioning vale etc, get in & try it.
go for it!! good luck!!