the formula you are refuring to is rpm x displacement (any given rpm) over 3456 (number of cubic inches in a cubic foot (1728) x2)

but in order to use the formula you would have to know a bit about ignition theory and would only be usful after three or more other formulas are done ie; piston fpm (stroke in inches x rpm over 6) and indicate torque (5252 x horsepower over rpm)

but rather than do that i would just go to a dizzy shop and get them to go 15 at idle (wich with quads would be 1000\1200)
and 35 degrees all in at 3500. it may prove better at 18 at idle but the motor might not start at that