Building a rear...

I'm converting to 5-lug on 87 coupe. Here's what I'm doing:
Junkyard 31 spline from an Explorer. Gonna rebuild it and pack it as tight as possible and get the heavy duty S spring.
Superior 31 spline 5-lug axles. Got them from Summit with bearings and lugs for about $250. Best price I could find.

A friend of mine has this same setup and has been racing it for two years now running mid-low 11's.

If you're keeping the same gears that are already in the 8.8, you'll need to shim the differential and check for backlash when you reinstall it. For that you'll need a dial indicator.

If you're replacing gears, that will take more work, but can be done especially if you have it out of the car.
Best way to do that is to put the rear in a jig to hold it still though...

the later model exploders, I mean explorers came with 31 spline carriers and axles (later 90's, w/towing package). The carriers aren't super expensive, and they can be rebuilt. The ez lockers, tru traks, ck out www.randysringandpinion.com for more info on the different types of diff's, this should help you make your choice.

as far as packing the diff tighter; be careful, if you put too much into it, you'll end up with axles that barely fit into the carrier and then it'll end up eating itself...I'm going through that right now, so I found a NIB 03-04 Cobra carrier off eBay for $175, and on payday grab a set of superior axles from Summit...then go spend another $225 at the shop having them install all the parts.

I would do it myself, but honestly, I'm getting sick of being covered in 90wt and smelling like crap for two days while it wears off