This came up over in the Shelby section, as part of a different discussion, and thought I would visit here with more of a focus.
Discussed the difference with Charles and he offered he had seen four variations but those included service parts also (NOS)
So would like to at least focus on the original assembly line ones if possible
So here are examples of what I found in my pictures. They (so far) have fallen into a pattern with no holes being the earlier version and the lower hole in the later with exceptions which might be a result of a rebuild or a fake/reproduction that got installed on the car
Carb #1 5R09K2141xx
Carb #2 5F07K28180xx Bad angle but appears to be no hole
Carb #2 Reported new take off but didn't list year or plant
Carb #3 Stamped 6Z C
Carb #4 Stamped 6Z C
Carb #5 6R07A1590xx
Carb #6 6R07K2040xx Rebuilt but original to the car -Know the car well
Carb #7 6S105x
Carb #8 6S117x
Carb #9 6S120x
Carb #10 6S145x
Carb #11 6S200x
Carb #12 6S208x