I have a new old stock Michigan M70 aluminum propeller for the 1940s era Muncie/Neptune Alternate Twin 3.5 hp models from about 1941 to 1948. It is listed as 6-1/2 inches in diameter and 5 inches in pitch. Comes in the original box, which is in pretty good shape, too. Asking $50.00, postage in the U.S. included. Photos available upon request.
Email: csr112-n AT twcny DOT rr DOT com