I only have an engine, no bike. I picked the engine up with some NOS parts for $50, so I thought I'd rebuild it. The right side crankcase cover has no numbers stamped on it at all. Just a raised blank area where numbers should be. It does have the 3 speed transmission though. I noticed in the parts manual that the early cylinders had the screw on collar type of exhaust attachment and not the bolt-up type that my cylinder has so I thought maybe mine wasn't an early version. Maybe there was yet another version of the motor between the early ones and yours???
Otherwise, I have no information on the engine.