Before I bought my 8.5 core (looked like scrap) I took a tape measure to the 7.5 to get flange to flange, bracket to bracket, perch to perch, etc. The 8.5 fits the same linkage, so all the "reference dimensions" will be the same as the 7.5.Axle tubes shortened, trailing arm mounts added or relocated, and leaf spring perches removed. There may be more to it but these are the basic mods that might be visible on an 8.5 out of a pickup or fullsize car, that was converted to fit in a Gbody.