[Gene1949]

absolutely use manifold vacuum. Much improved cooling at low/cruising speeds and drivability at any speed. And yes a measurable increase in fuel mileage. Every manufacturer used a vacuum advance of some sort before the advent of computers.
My curve;
total Mechanical including initial: 16 degrees at 1800 RPM. max 22 degrees at 2300rpms. Credit due to one of the wiser heads here (Gramps I think) who developed this curve after much testing
vacuum: 14 degrees @ 15". I used the vacuum level at 70 mph as a setpoint. You may have to change that a bit as that works with my car at this elevation.