No.
Those may be casting numbers for the end shields.
Squarebacks start in '72
The p/n was stamped. There's a picture in the sticky thread showing where to look.
Starting in '74 they got metal tags also shown in the sticky thread.
I don't have anything like a complete list but for '74 a production '50 amp' with the 2.75" double sheve pulley was p/n 3755 411
Lester 7509 or 7509A is a common crossref for replacments. 'Rated 60 amps' FWIW.
