There is a rather bulky shortcut to the electronics problem, but it turns it into a programming problem. If you can live with a laptop computer for a display then check out the diy mpg gauge (for fuel injected vehicles). It would be good for prototyping if nothing else and could theoretically be taught to read drips, marbles, throttle position, vehicle speed, whatever.
http://www.gassavers.org/showthread.php?t=4250