Hi!
As your engine has no reduction drive, and is more or less like an ordinary poppet valve four stroke, you need a either a 10x8, 10x9, 11x6, 11x7,12x5 or 12x6 3-blade prop.Best props on the market are RAM, Graupner Cam-prop and APC. But of those only Graupner and APC makes 3-blade props.