Personally, I would just swap to a 9". I had a shop fab up a housing for me for like $200 and got a rebuilt 3rd member with posi and the gears I wanted on ebay for $400ish. Reused my 8" axles/brakes/etc and had myself a cheapo rearend. You sound like you're looking at not much less than that to put that 8" back together.
Exactly. Why keep fooling with an 8-inch when you could install a 9? --Break an 8-inch once, shame on it. Break an 8-inch twice, shame on you.
I've seen claims by some on the forums that a 9-inch rear is 75-100 lbs. heavier than an 8-inch.
Contrary to popular belief that the 9-inch rear end is a mega-heavy pig, in reality a 9-inch drum brake rear --like a '57-'59 Ford passenger car 9-inch, is only 24 lbs. heavier than a comparable width '65/'66 Mustang 8-inch rear. That doesn't constitute as being excessively heavy in my book, and certainly is nowhere close to the 75-100 lbs. more claims by some.
Even the '77-'80 Versailles factory disc brake 9-inch rear end, considered the "heaviest of the heavy" is only 45 lbs. heavier than the '65/'66 Mustang 8-inch. --Still, nowhere close to the 75-100 lbs. mark.
In more recent years, companies like Curries has produced parts to beef up the 8-inch. However, the parts to do this are
very expensive and in the end, it isn't any stronger than a run-of-the-mill factory-stock, entry-level, wrecking yard 9-inch.
Weight comparison between 8-inch vs. 9-inch in following link [scroll down page to "FORD REAR END WEIGHT COMPARISON"]
The Ford 9-inch Rear End
..If you can't locate a 9-inch at the salvage yards, you should have no problems finding an 8.8" that could be modifed to work. It isn't as strong as a 9-inch, but is much stronger than the 8. Then again, there's always the aftermarket to build a complete 9-inch assembly. Probably won't be cheap but in the end, you'll have something bullet-proof that isn't going to go tits up on you.