Aspen Disc Brakes

Run the Aspen/Volare spindles.

They work better in some areas of the range and worse in others in comparison to the A body stuff. Bill Reilly at Big Block Dart did a test of the two spindles.

I've run MANY A body cars with the FMJ spindles with no failures in some extreme duty, far worse than a normal street car would ever experience. Never had a failure and no bump steer issues.

Your needs one of the following:
for the current arms, a Ball Joint sleeve installed that Dr Diff produces, the upper threaded area cut out and install/weld a fresh BBJ diameter sleeve (stockcarproducts)

or

a set of 73-76 a body upper arms.