Looks like a rebuilt carb to me,, as whats that sticker on the fuel inlet..
Agreed. I suspect that is how it ended up with an incorrect base. Since starting this thread I have discovered the correct casting number of the base/throttle body for the 7028264 and found a nice one to replace this one prior to getting it professionally restored.
I've loosened old horns before by filling the inside with penetrating oil and letting them sit for a couple days. Sometimes it works, sometimes not. If they won't make any noise they are probably shot.