The Gbody uses a four-link rear control arm setup. The upper bushings are centered over the axle tube centerline. The later-model
Caprice rear and 64-72 Chevelle axles are wider and the upper bushings are centered slightly forward of the axle tube centerline, so they are not bolt-in. I have heard there were special aftermarket upper arms made a while ago to use a Chevelle 12-bolt in a G-body.
The
Grand National and
Hurst Olds use an 8.5" center section that has the exact G-body control arm mounts, but they are hard to find and often hammered after 30 years. The F-body uses nearly identical lower control arms as a G-body, but instead of upper arms, they use a torque arm that connects to the transmission tailhousing, and panhard bar to locate the axle left-to-right. See PontiacGPs photo. The S-10 uses leaf springs, and there is no easy way to add the upper mounts onto the cast iron center section.
So, keep looking for a GN 8.5 axle. Or keep a spare 7.5 G axle around. Or if your pockets get deeper, go with Ford 9". The reason they are the go-to axle is that they are durable (used under half-ton trucks and under 5500lb Lincoln Continentals). The 9" housing itself is made from formed steel, so it is easy to weld in G-body bushing mounts. Plus 9" axles use pressed-on captured axle bearings, so no C-clips to break and lose a wheel under abuse.