Cool finds! Interested to see what you make with them :-)

Thank you, Dan!  I have taken them apart to see how they work and FWIW, mechanical  gauges became a whole lot less mysterious to me in the process.  I will definitely repeat said process and update this project with the info.  Basically, I just need a max of 20 psi for the fuel pressure, the other two can be manipulated with fairly gentle vacuum and compressed air.  I just don’t want to fill the bellows in them with any kind of fluid, not at this point.  I’ve got some decent ideas on producing the needed pressures quietly (quiet being key, I don’t want to hook them up to my 90 gallon compressor :/) and hopefully some actual progress soon.

Seeing how you control these gauges will be interesting. Here's hoping you can make them usable without having to gut them and put in steppers or servos. Good luck, and keep us posted.