You could also look for a 8.5 rear from a 73-79 Nova. They bolt right in without having to cut the perches. They are 1" shorter than the Firebird rear but the spring perches are perfect and most are already set up for multileafs. I just finished installing an 8.5 from a 79 Nova with posi and it fit in no problem. You will have to account for the 1/2" difference on either side if you have aftermarket wheels but the Rallys fit with no rubbing at all.