I gave the 8.75-vs-Dana60 choice a lot of thought on my wagon project, and the difference was only about $200 between narrowing & bracing an 8.75, axles, diff housing, caps, SureGrip, bearings, & gears vs a Dana with new good axles, SG, bearings, & gears. The car's just a footbrake BB deal, but with 3700-3800 lbs & slicks, I figure that's money well spent.
I have enough things to worry about already.
As a kind of bonus, that A-body rearend is pretty valuable, judging by the last time I needed one.