Hi Karl,
Here are four side by side images of an original 5A HiPo lid base next to several reproduction bases. The easiest way to ID an original to a repop is examining the breather nipple. As in the OEM stuff, there are variation in the reppop world too. There are three repops compared to the same original.
You can see quickly the differences. Yours looks like an original.
Another difference, but harder to confirm without a accurate measuring device, is the opening on an original is slightly larger than the reproduction. The reproduction I photographed just barely fits onto a 4100 Autolite ZFC carburetor, but the original fits with a little more clearance. I will need to find my micrometer and post the actual dimensions.
Good deal on your find.
Cory