When I first purchased my 1970 Malibu it had a completely shot front end, but came with rotors, calipers, spindles and backing plates from a '78 F-Body (Trans-Am) car, as well as an aftermarket convresion kit. I used this kid and my car works great. It brakes very well and has the improved geometry thanks to the more modern F-Body spindles.
The kit allowed me to use my stock A-Body upper and lower control arms, but there are a few points which make this option undesirable:
I am frequently asked about this conversion and figured I'd never get the proper information until the May 1999 issue of Chevy High Performance in an article entitled "Great Brakes." This article details three different Disc Brake conversions. First is the stock '64-'72 Disc Brake setup. I won't deal with this one at all since if you can't find these part numbers, you aren't yet worthy of your A-Body. The second conversion is for the F-Body front disc brakes and the third is for '77-'89 B-Car (12 inch) brakes. I won't deal with the third option either, as it wont allow you to use your stock rims. If you want info on this, get ahold of the May 1999 issue of CHP.
This conversion will require the use of tubular upper control arms from either Global West Suspension Components or Hotchkis Performance. These will cost you a few sheckles, but are well worth the investment for reliability, and will not require excessive shimming as the stock upper control arms would.
Here are the parts you will need for this conversion, given in Raybestos part numbers:
Hope this helps out with you folks and your projects. I haven't used this kit yet but plan to whenever I get around to the front disc brakes on my 1969 Buick Skylark.