I'd suggest getting 31 splines. I ran all last season inculding spraying outta the hole on et streets on 28splines and mine were ok. A few weeks ago a group of us went to the track about 100miles away. One of the guys brought his mach1 down just gears, 315dr's, and exhaust. 3rd pass the axle broke. Took out the carrier and the driver side axle along with the brake caliper mounting bracket. Then we had to wait for the wrecker and tow it back to his house 100miles away.
In order to do a 31 spile you'll need the diff (exploder's are cheap about 150bucks or less), and axles.
If you just want to do the axles the diff may still go but you'd need the axles.
Of course with either of those your going to need, diff fluid 2 bottles (8.8's take like 1.8 qts), friction modifer/additive, and some rtv for the diff cover.
As for axles everyone has the ones they prefer I like my Moser's I ordered from a local dealer and they were made to order, not sitting on a shelf in some big wharehouse. Of course that added a few days to the order but oh well.
