With your help, I've narrowed this engine down to two choices:

It's a Herkimer OK Cub, and either a .29 or a .35 made in the mid 50's.

Please tell me how I tell the difference between the 29 and the 35.

I measured the diameter of the piston. It is 0.7 inches. Is 0.35 the radius of the combustion chamber/piston?

I had someone tell me that the 29's had red trim and the 35's had gold.

Thanks!

Bob