10sec340,
Mark Williams makes the billet steel caps, and billet adjusters. I've seen the oem adjusters blow out, also. Like Adam said, the next weak link is the small diameter ring gear. And not to mention the flimsy 8.75" housing (ring gear deflection).
I've built both 8 3/4" rears and danas for drag cars with big blocks and trans-brakes. You can be on the fence real easy. Losta power like you make, and the heavier cars are brutal on the 8 3/4" rear.
FWIW, my red b'cuda went 10.00 @ 130 with an 8.75" rear. It weighed 3025, with 500cid, and a brake. I used the MP aluminum 3rd member, and backbraced the housing.
Now, I deal with this all the time with my customer's when they break their 8.75. By the time it's all said and done I could of bought a complete dana 60 with disc brakes and had money left over vs. modifing the 8.75". More times than not, we upgrade them to the dana!
Good luck getting it fixed, and goodluck with your racing!