The engine design IS important.
But the WEIGHT, FRICTION, STREAMLINING & RELIABILITY could be more important.
Try to COPY the winner with the highest MPG. Improve from their success.

Since you are only operating at idle & WOT, a carburator will do almost as well as a $ 3,000 electronic F I & ignition setup.

PLUS.

It is a Hell of a lot more reliable than a prototyped computer program. Most "Did Not Finish", are due to the computers & wiring, failing in the final runs. A carb only can have at MOST is 4 jets for your use. Idle fuel & air jets.......WOT fuel & air jets.
Know the temperatures and humidity at the place & time of year of the contest. Set the carb accordingly. Carry 2 different setups of jets for a worst case ever run condition. You can absolutly change jets faster and more reliably than a programmer can. Just have the 2 different complete carbs to cover conditions. Most reliable way.
Change the carb to the condition.

Planning for reliabilty always beats R & D.

Dumb luck overrides either one.

# 1 priorty is to make dozens of runs with absolutly NO problems.