I would like to suggest two axles you never see in a A body.
1. Jag IRS
2. Ford IRS
The jag IRS you could get from Pull apart in Atlanta for a low cost. Very easy to narrow. Easy to install. Inboard disk brakes, Set up for quad coil over shocks. The center section is very close to a gm 12 bolt rear axle. MADE IN AMERICA.
The bad part about the jag is the bolt pattern is 5 x 4 3/4".
The ford will cost more but its lighter and has the correct bolt pattern.
The came in some Mustangs, some Thunderbirds. and some Lincolns.
The Ford is made from a 8.8" axle.
http://home.bresnan.net/~dazed/JaguarIRS2.html