Could you turn down an OEM disk for the hub and use the disc assembly with your adapters? I'm not a big fan of aluminum in that application. Will your adapter work with 73 up A Body knuckles?
You can do anything you want (or afford). Turn down a stock rotor to make a hub or make one from steel or start with a drum brake hub and go from there, etc. It is just time and money.
The bolt pattern is the same on the A body knuckle as the FMJ knuckle but you might have to grind some clearance since the A body knuckle is shorter and heavier.
