Originally Posted by joe_padavano
The 84 Hurst/Olds (not the 83) and the 85-87 442s came with a 3.73 8.5" axle. The 85-87 GNs (and possibly turbo T-type cars) came with a 3.42 8.5" axle. Those are the only bolt-in 8.5" G-body axles; all the other cars came with 7.5".
Also expect to pay $800+ and you'll prolly need to go through the posi unit - if - it has one (some didn't). I'd look at finding a bud who can weld and building up an Explorer 8.8", you can find one with the right gear and a locker (which can be rebuilt for < $100) and have the axles and drums redrilled for about half that...