I have flown my Four Star 40 with a .46LA and it flew great , just not much vertical pull. I bet that a ball bearing .36 would fly it pretty similarly, and the weight is pretty close as well.

You would probably be disappointed in the performance, though. And I don't think you can avoid notching the cheeks for the muffler and needle valve. It really doesn't look bad.

I now fly mine with a .55AX and it is a rocket.

Good luck