8 3/4" How Strong?

The 8.75 is capable, but by the time you build it stout enough, you'll have enough money invested to more than cover something like this fabbed (and much stronger) 8.75 housing from Moser:
8 3/4 Mopar Fabricated Housing & Axle Package - Moser Engineering
And you still retain the easy carrier/gear interchangeability of the 8.75.
Or just build a Dana 60 if that doesn't matter to you.