I picked up a complete engine and had some difficulty IDing. There are no date codes stamped in the usual place. There are no raised letters on the bell housing, just a lot code. The one thing the block does have is a raised intake surface (see photo). The heads have a lone A cast into them, and 81A stamped (1938-1941?). All the cylinders are sleeved and are at 3 1/16. The stroke is 3 3/4. Given all this, I'm guessing it is a 1941 WWII military engine. Am I close?