i have bought a second hand pylon engine model no 3070 with a pipe pt no 3247 and what i will describe as a grooved manifold. i am grafting this into a mig17 ish plane and was wondering what props suit this engine and pipe. also do i need to trim the grooved header pipe. looking through the old posts a prop like 8x8 or 9x7 looks posible but will thses allow the engine to use the pipe to its maximum. i have no documentation on this engine