You might try this site:
http://www.asecc.com/The bore and stroke, and the "5" on the crankcase, would be consistent with it being an old Model 5, but it looks quite a bit different and I can't find any reference to them being made after 1957. That means it didn't have either a 5-sprag starter clutch or even a recoil starter. However if you fish around on that site you'll at least be entertained, if not enlightened. I think your engine was a successor to the Model 5S, but I think the 5S had a low fuel tank and a suction carburetor, like most of the 1960s, 70s and 80s small B&S engines.
