Gears & Axles - Need help finding a diff rebuild kit

I have a 99 z28 6spd with ASR. My bearings are going out and the rear is howling. I looked on speed-eng.com and they have complete rebuild kits but one is for a 8.5" 10 bolt and the other is for a 7.5" 10 bolt. Which one do I need? The brand is ratech. Is there any other rebuild kits that you would recommend?

http://speed-eng.com/store/ratech-deluxe-gear-installation-kit-bolt-p-10007.html

These cars came with a 7.5". The stickies at the top of this section of the forum have a lot of good info that may help you out. Bob

I got the ratech kit from ws6 store when I replaced all my bearings. Came with everything I needed and then some