Are LS1 rear wheel hubs smaller than on LT1's?

I've acquired a set of '99 Firebird twisted 5 spoke wheels and they mounted on the front hub fine, but did not want to slide over the hub on the rear without a little grinding to the wheel. Is this normal? Also, I seem to have more threads available on the front wheel studs than the rear for the wheels, is this normal also?

Yes they are smaller on the 98-up. I ran into the same problem when I put 98-up ten spokes on my car.

So grinding them down a little is the only solution to get them to fit I guess? What about the wheel studs? Are there less threads available on the rear than the front?

I had the same problem when I had my 95 Z28 and put on some "take-off" Firebird 5 spokes I got from SLP. I just used a file on the inner hub area and then used a small amount of anti-seize to make sure I wouldn't have any problems when I would go to remove them.

As far as more threads on the studs, not an issue at all.

I had no problems with the studs either..

I had no prob on my threads either on my red Z but I took the rims to my buddies machine shop and he grinded an 1/8 of an inch off(equal to the edge that sticks off inside).

I had that same problem with my C5 wheels. I just took out the Dremel and took a little bit of metal from the inner hub on the wheel.

I just installed a set of 2002 17x9 WS6 wheels on my 1995 Z28 and they slid easily on the rear hub.

Doesn't matter anymore, my gears broke on me. I just acquired a 2000 rear axle with LOW miles on it, so no more problems with hub or studs.