When I restored my 74 Rallye I went through 7 bad alternators from Advance Auto. 4 were stripped castings though. After I went to NAPA and got a good alternator I still had an intermittent ground on the voltage regulator. Symptoms were overcharging from the alternator.
Check battery to body, K-frame, engine and firewall ground. I tried to keep the paint pretty on the firewall and run dedicated ground wires. It didn't work out so well. I finally cut the paint and left the dedicated grounds. Now it works.