Let's say I wanted to convert to JL8 specs and could get a big car 12 bolt to use for this. I assume a few things-

1) The brake flange is the correct one to bolt up the Vette caliper bracket
2) The rear needs to be narrowed 1/2" each side
3) Need axles for the smaller bolt circle
4) Leaf spring brackets need to be welded on
5) I get a bigger better flange axle bearing?
6) 66-70 Impala, units are the best setup, no obscure one year bearings.

I read once that there were instructions from the factory for this? Anyone have a copy to share? Are there any other details to this swap?

Thanks!

1) the brake flange should be the same
2) deeper offset wheels take care of the longer axle
3) i think most of the big cars except for wagons had the correct bolt pattern. i know the 67 Impala 2 door i had many moons ago had a 12 bolt with the small bolt pattern
4) this is easy- use MOPAR universal perches
5) dunno
6) dunno

Some big car rears may be more than 1/2" wider.
The bearings may be larger, but what axle would you use in there?
GM talked about using them and listed axles in their parts book but they are long gone. You are better off either fitting std axles and bearings or going to Ford bearing ends that use the GM bolt pattern. BUT! the JL8 rear used a different pattern than drum axles anyway. You need basically a Corvette pattern on there.
David

Thanks as always guys. I'm bummed but maybe I can use other options. If I were to get a Moser rear instead, I might be able to find appropriate brakes from MP or SSBC

Time for more research. I appreciate the no-nonsense David!

how about a Moser rear end with JL8 bolt pattern

I'm wondering the same thing Mark.. But I have not contacted the yet.

Using a big car 12 bolt as you suggested would work well, just narrow it and get housing ends, or weld back on the old ends but change the flanges to JL8/Corvette. You can look for bearings to fit the big car ends that will work on Camaro axles, or just get aftermarket ends.
David