Hi Karl,
You are welcome for the information and glad to help. That is what this forum is all about. On the four base diameter opening's for the carb, I found the below inside dimensions and how well they fit on a Autolite 4100 ZFC carb.
5.05 inch (Repop, will not seat onto the carb. Possibly an older repop.)
5.08 inch (Repop, barely fits, requires pressure to seat, the radius on the lip opening helps.)
5.10 inch (Repop, fits, but not by much, the radius on the lip opening helps.)
5.15 inch (Original. Goes on nice.)
The OD for the ZFC carb is 5.10 inches. This helps explain why the repops are challenged to install.
I hopes this helps others properly ID a correct HiPo lid base.
Take care
Cory