This is an old-school question. It was a non-stock DIY deal.

Does anyone have information on the old steady-vacuum, not steady-speed, type of engine control? I hesitate to call it cruise control.

This is a setup that allows you to set an automatically controlled vacuum point above the power-valve setting, running the engine gently for economy. A diaphragm controlled the throttle to maintain something like 10" of vacuum, no less.

For those of you who have never heard of it, the system only works in no-traffic situations, and slows greatly up hills, and usually goes too fast down-hill. Clearly, it is for long distance, middle of the night driving. No, you probably don't want one.

I spent an hour Go*gling it, and wasn't able to find anything. I would bet there is an old P*pular Scienc3 article somewhere. Goes to show how marketing-oriented our search engines are now-days.