Locker or sure grip for 8.75? What are you running in your hot street/strip car?

That 8 3/4-489 you've got should stand up to a 500HP auto car no problem. Go through it with a fine tooth comb and if in doubt throw it out. Pay particular attention to the housing bearing saddles and have the caps die checked for cracks. If you're running the cone type check that they haven't worn to much into the housing and if it's the clutch type replace the discs and plates. Then drive her like ya stole her.
I'm running dam close to 500 thru a 742 and haven't broke er and that's with the occasional stickies bolted on. (drives the street stang drivers nuts when they're spinning and I'm not)
http://www.moparts.org/Tech/Archive/axle/13.html

Terry