Whats is worth 8 3/4 with suregrip, drum to drum, 3.91's

I'd say $700 - $1000, depending on how badly someone wanted it. I have a bare housing, SBP axles, and backing plates for an A body that were given to me. I've had quite a few people try to by it, but it's not for sale. Regarding the Dana 60 comment above, I have been able to buy complete Dana 60 HD rear ends from 3/4 or 1 ton trucks for $50. I have one in the garage that was, again, given to me.