Billy,
The Alternator is a Pontiac application used on Firebirds and GTO's with A/C or Rear Defroster. As you stated, it was assembled on October 21st, 1971 for a 1972 car.
Also, the water pump is actually 6263701. Yours looks to be L61, so that would make it a December 6th, 1971 build, for a 1972 car.
Ed