i dont know how well a belt start is going to work on a big 4 stroke. i use the ofna pink starter box with the big 12v motor and it struggles on the 56. most of the time i have to roll the motor just past tdc to get it so itll crank it over. im just thinking a belt might just slip or break with the amount of compression. maybe consider doing a starter wheel on your airplane starter.

just tossing some experiences out there.