>> “This ad dates from 1963 or before (no zip code in address)” <<
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Earlier than that, pre-m14 too. (”Current rifle of the US armed forces” per the ad)
I went through Marine Boot Camp in 1960 and we were issued brand new M1 Garands. We kept them until 1963 when we were issued M-14s.
If you have an interest at all in an M1 Garand check out CMP for rifles and ammunition. They probably have the best deals going unless you know someone willing to let one go below market price. CMP has Garands in varying condition starting at $495. Feedback on their forum is excellent.
Civilian Marksmanship Program (CMP) Sales and Catalog