Have a look at fuel flow meters for marine engines ($$$, though, such as
FLOSCAN). The trio of driver gauges would be:
Fuel Flow
Vacuum
RPM
Additional would be:
Airspeed
Depending on the car there are (or were) spark timing adjustment boxes (MSD, and others) where one can advance or retard ignition timing. With the above gauges (and maybe a knock sensor) can can "lean out" the engine for best cruise parameters.
Some of the "feedback carbs" worked in a similar manner.
What kind of car is it?
EDIT: I see you are aware of marine fuel flow meters.
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