I have not seen an 8.5" in a G-body wagon yet and be careful as most full size wagons use a unique 10 bolt that looks like an 8.5" but is actually an 8.875". I have an A-Body (75 Olds 442) rear end in my 81 Malibu. Not exactly a direct bolt-in deal, but it can be done. The person who did mine fabbed 9" housings on the side and he had a jig set up mimicing the actual car. From there he attached the lower mounts and spring pockets. Then the upper control arm need to be shortened and staggered outward to make up for the added width of the center section. The rear end is 3" wider than stock which can accounted for with additional back spacing. I had my Olds Ralleye wheels widened inward 1.5" to make up the difference. I have copied a set of these for a friend and they worked out great. Also, don't forget the coil springs from a
Caprice Wagon as they are a cheap alternative to an after market spring - ride height in virtually unchanged, but the rate is much higher.
I'm sure the same technique can be used on a '77 & up
Caprice rearends as well - some of these have the 8.5" and are probably one of the most plentifull cars in scrap yards.