OK this rookie would like to know if he got two identical carbs, why you can't swap bases.
If one base had the vacuum hole, and the other did not, then the carbs are not identical
Joking aside, there may be other consideration rather than the hole.
Assuming this is a Zenith 28 or 228 series, there are dozens of varieties in each of 6 different sizes. And there are different throttle bores within the same S.A.E. size.
Unless the carbs are identical by tag number, BAD idea to swap castings (unless you have prints for each carb, and the castings in question have exactly the same part number). Obviously, in this case, they would not have the same part number.
Yes, sometimes it will work. More often it will leave one with a carburetor "gremlin" that ends up with an eighty post thread on one of the automobile forums.
The position of the hole is more important than the size of the hole.
No comment about whether of not vacuum advance is necessary, not my area of expertise.
But if I were still doing carbs, and someone sent it to me like this, I would take it to the local welding shop, and have the entire hole filled with brass; then correctly machine a new hole. And charge accordingly.
Jon.
