Nope did not have to modify the 8.5, it bolts right in. Spring perches are identical, but some Novas had single leaf, don't get those! the Nova rear end is exactly the same as a first gen Camaro 10 bolt rear. The Nova rear is 1 inch shorter in width, but I don't see a difference. I pulled the backing plates off the original rear and just bolted them back on to the Nova rear. They bolt right on, very easy! Here's a good link on 8.5 10 bolts http://www.camaros.net/forums/showthread.php?t=188370

If you use a later second gen driveshaft like I did, you will need a conversion u joint at the rear. the Precision U joint p/n is 372.
Wrong! The drive shaft I had was actually from a 73 FIrebird. I turns out that the read had a 1310 u joint and the front has the 3RL/S44. Weird, but that is what is in there now. Sorry for the confusion