I agree with Doug...get those numbers off the bracket/mag....
The new variations of the "big yellow book" have an appendix of these numbers and what they went to.....it would enable you to narrow it down quite a bit I would suspect...if you don't have the book with the numbers, post them here and someone will be able to look them up and tell you which mfr it was that used that one.
Looks pretty rare whith that hopper opening and the main caps on the back side of the frame. I have seen one other engine with this style mains, (I don't remember the hopper), and no one knows who made it either.
I have seen 2 other engines including the one Ray mentioned with the crankshaft and flywheels hanging out past the base with the bearing caps taking the force of ignition, not to mention the shear force of the flywheel crankshaft weight. It looks like a weak design (but great for a collector) My theory is, the first few engines made had a name tag but after the engines started self-destructing from the design flaw, that they quit putting their name on it so it would be hard to find the maker to complain.
A good friend of mine had an engine just like this for many years. Dont know who got it after he sold it but anyway it is an American Boy engine. My friend searched for many months to identify his and finally spoke with someone who had an original booklet showing this engine. Probably about 1 1/2-2 h.p. it is very unusual the way the main bearing caps bolt on. I have a picture of his engine somewhere, will try to find it and post it here in a day or so. Very nice engine!
Hi, Chuck, I think it is a George Miller made in Iowa for Thomas Jeffery, the builder of the Jeffery Car, in Kenosha, WI. I just saw an original one at a sale last year. It was closer to you than me. Hope this helps, Jason.