Series 6 from 1965 had 77 cards in the series, so SPs exist. Reconstruction of the slits will be exceptionally difficult because significant miscuts are scarce. However, there are some available, so I am trying anyway.
Here is some additional information in case anyone wants to chime in.
From what I can tell, Topps used the following pattern for the locations of the checklists in each series:
Check 1 (both versions) were in C11
Check 2 was always in C2 (both 1st & 2nd series printing)
Check 3 was always in C11 (both 2nd & 3ed series printing)
Check 4 was always in C2 (both 3rd & 4th series printing)
Check 5 was always in C11 (both 4th & 5th series printing)
Check 6 was in C2 (5th series printing)
Check 7 was in C11 (7th series)
So, I would expect Series 6 (# 443) to be in Col 2 while Series 7 (508) to be in Col 11 for the 6th series printing.
I think the series 6 (443) printing variation has the nearly complete m in #481 (series 5 printing of 443 has the mostly cut off m). The series 6 printing of series 7 checklist (508) should be the larger print version.
And here are a couple of miscuts, offered as a tease.
1965_451_MC.jpg
1965_482_Priddy_above_Owens.jpg
1965_485_Fox_bottom_edge.jpg
1965_Banks_V475_510.jpg