I'm building a 64" wingspan Stearman PT-17. An old Sterling kit as a matter of fact. Ha, I should say that I am building the plane from scratch with the kit as a guide since most of the kit is unusable, it being 40 or 50 years and all. Anyway, I am wondering if anyone has any 4-stroke engine size formula or recommendations? I typically use 2-strokes and the kit calls for a .56 to .65 2-stroke but I would like to use a 4-stroke in this plane. I have a saito .80 and a Saito 1.20, but it seems to me that the 1.20 is too big and the .80 is too small. Any thoughts?