I think that you have been misled about the Zeniths. IMHO they work well.

I think your biggest challenge is that in this day and time there are more people that understand electronic fuel injection than there are that understand carburetors.

Every carburetor has basically the same subsystems. If you understand these subsystems, you can reverse engineer most any carburetor.

I have not had my hands on a set of Zeniths in probably fifteen years, but as I recall, the biggest challenge was getting them off and on. I had to make a special wrench to reach underneath.

I think you should try to find an old timer that has rebuilt and successfully tuned a zillion carburetors. It doesn't matter if he has ever seen or heard of a Zenith. If he understands the principles of carburetion he will be able to figure them out.

I still have a pair of carburetor kits for those Zeniths if you can't find them anywhere.

Good luck,