Do it the way Carter did for years- - - -use a mechanically-actuated metering rod and eliminate the vacuum piston altogether. With a few thousand hours of R&D and a few million dollars worth of tooling up and manufacturing, you could probably convert Rochesters to use mechanically actuated metering rods- - - - -or just run a Carter carb in the first place.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!