RE: Wath for cox is this ?
Andry,
Well for a better name lets just call it a Babe Bee! I looks like it's a mix and match of parts from different years but that is no big deal. Note the narrow neck crankcase and the Thimble Drome script on the fuel tank. That makes it an early engine but the cylinder is newer. Check and see if the cylinder has a small number stamped on the outside below one of the exhaust ports. If it is a #1 that is a twin bypass cylinder and will offer a bit more power than a #2 cylinder which has only a single bypass port.
Later,
Tim