When cruising, keep the vaccum as high as possible for the best mileage. Hot Rod did a build on a Monte Carlo, years ago. Used a vaccum gauge to determine the best cruising speed. Also, the old Impala SS's had a vaccum gauge where the clock would normally be. The tach was mounted on the center console. A/F meter would be a good choice too.Tell me more about the vaccum guage.
I had thought about installing an A/F ratio meter to let me know when I'm running rich or lean.