There's a guy on the forum here that rebuilds brake and suspension parts. I bought a few sets of reconditioned kelsey hayes 4 piston disc brake set-ups complete from him, just attach to upper and lower ball joints. If he still has any, it's reasonable to get them. With the Kelsey Hayes, you can keep it with the stock 4" bolt pattern. The KH discs were stock from 67-72 (I'm not sure about the early A's)
In 73 they switched to the 4.5" bolt pattern single caliper disc brakes. They are common with the B & E body front disc brakes. If you want to convert to 4 1/2" bolt pattern, then go with the single piston calipers. They will require going with the 73 and later upper control arm which will bolt in place of the early one.