I can't answer your question but I can share your pain. I too went thru countless "professional" rebuilds, including some that added the ugly external balancing hose for air filter use. Finally, I coughed up the bucks for one of the brand new Mark reproductions of the Zenith 1, which I assume the carb you are asking about is a modification of. After returning the first one because it refused to run, the second one was well worth the money--I drove it for several years. My problems were gone, EXCEPT for vapor lock, which eventually drove me to the final solution, which you might also want to consider:
This is a more modern--1980's vintage--Zenith made/modified for the Model A. Vapor lock problems are gone and it's impossible to stall it on a hard stop. And, it's balanced internally for air filter use, although it's not easy to hang an air filter on it. ALso, need to modify fuel line or connections for pipe thread fitting.
Of course, many Ford Barners will insist that your stock Zenith would work great, if only you had it correctly rebuilt, like THEY did--and it will never vapor lock--and it will never stall.
Steve