[QUOTE=
I just picked up serial 906xx. Looks like sometime in the mid '60s.[/QUOTE]

Serial number 90679 shipped in June 1967 but #94036 also was shipped in June 1967. This is a good illustration of Smith & Wesson not shipping in serial number order.

Best estimate on your M41 is late spring to summer 1967. Only a letter will give an exact date.