Keeping everything in the driveline aside from the engine stock, what will break first? Drag radials, full slicks, street tires, what is the weak link in the driveline?
I use to think that axle shafts would be the 1st thing to go, but that was before I saw DALE ROYSTER's car and what it does at the track and how hard he launches it with the stock 8.8 28 spline axle shafts. He leaves the line at 5,000 rpm's with M/T ET Streets and hasn't had a problem with the rear end. YET! I'm not saying it's going to last FOREVER, but it's held up so far. Not sure how many passes he has, but I saw him run 12.1's and 12.2's @ 114 all last weekend.
BTW 31 splines (or more) to answer your ? FallenPhoenix.
A Ford 9in rear end setup would be the strongest way to go, but probably the most expensive as well. You can get by with just a 8.8in rear setup. Just upgrade to 31 spline over 28 spline and you should be fine. If you're going to bother with building up the rear end, you might as well do it all right the first time.
31 spline differential
Aftermarket differential cover
31 spline axles
New Bearing & seal kit
Aluminum Driveshaft
Driveshaft safety loop
If you have plans for gears, do them whenever all the other parts goes in. It will be best this way.