I would love to find the machine that opens and closes the vac advances, I have a few milk crates of bad ones I have been holding onto if needed to get rebuilt, one guy does them that I know of and not cheap either. 60 and up
Could you make one with an A/C vacuum pump, vacuum gauge and and a barrel valve to regulate the amount of vacuum?
Heck probably could use the a/c gauges with a different fitting.