The serial number should make it a 1940 model. According to Norm Swinford's book 411 single front wheel WC Speed Maintainer graders were built from '38-'41. If it has an extended front end with two front wheels (like the one pictured in the link) then it is a W Speed Patrol. 678 of these were built at the LaPorte, IN factory from 1940 - '42 then another 3073 were built in Springfield after the war ('45-'50). Both were based on the WC so engine hp would be the same. Does it look like the one in the link?