Jim, I'd have placed it a bit later: late 50's-early 60's? ...Splined prop driver... ...May also have cylinder exhaust opening narrower than the stack.

To A2Helos, just a check list: The piston has a low "fence" (baffle) across its top that goes on the side opposite the exhaust port. The head should have a groove to match the baffle. With those set right, the head fins run front to back, not angled.

A positive - looks like the head bolts were changed to Allen heads. Much easier to work with than the Phillips (or Reed&Prince?) originals.

A2H, luck!