Definitely best possible use for a stock Cub.
Oddly, Cubs can be made to run very well. Clean up the crankshaft porting, balance the shaft, clean up the burrs in the bypass ports and run high nitro and they will absolutely scream on small props. They have very low compression ratio, so a hot plug and hot fuel are tolerated very well indeed!
Oh yes, replace the needle assembly with one from a Cox ready to fly engine. A fun project, but not unless you really, really want a hot Cub just to say you have it.
I flew one at Taft on a 1/2 A Spacer, and walking back from retrieving the model one guy who saw the flight eyes bugged out and said “THAT’S A CUB?” Guess I got it right.
I was using 60% Nitro +P fuel, but that is what makes a Cub sing.
Or buy a better engine.....
Anyone want to run a Cub RPM contest? Now THAT could be a challenge. Say specify APC 5.5x2.5 prop and 30% nitro fuel. (Or higher if readily available). Don’t look at me, I no longer have any fuel stuff. Totally e-power now, but will happily talk to people in the real world.