Nick, that's one bruiser of an engine (and one very cute boy!)
One thought I had... You mentioned about it not needing a cast base, as the crank was high enough for the flywheel to clear. It seems doubtful to me that an engine with separate bearing supports would have been designed to be mounted to a wood base. That would be an open invitation to bearing misalignment from the wood moving over the passage of time and temperature/humidity changes. In addition, the flywheel looks small for the 2" bore size.
Could it be that this engine was pieced together from parts of one or more incomplete engines? If a cast base was lacking, perhaps they used a smaller flywheel to avoid the need for a recessed base. [ Guests cannot view attachments ] Just a thought. Practically speaking, the wood base should work pretty well, as long as the bearings are not too close of a fit.
A little more about D & M Model Engineering...
Two model engineering enthusiasts, Duane Dehnicke of Western Springs IL, and Ed Miller of Merrimac WI, started a hobby supply business Known as "D & M Model Engineering". Not sure when they started, but I acquired one of their 40-page catalogs (3rd edition) in 1986. They sold casting kits, plans, books, steam fittings, bar stock, fasteners, tools, etc., pertaining to the model engineering hobby.
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I met Duane (the guy on the left) at the NAMES show sometime in the late eighties. A nicer, more helpful person you could not hope to meet. He was a police officer in his full-time job. I never met Ed. He was much older at the time, and I imagine he's gone back home by now. Duane is in his eighties, and still selling model engineering stuff, though not as a regular business. He has a few items for sale on the Live Steam website:
https://selling.discoverlivesteam.com/search/?searchuser=Duane%20DehnickeIf I had more money, and more time, I would buy one of those power hacksaw casting sets, just for the fun of building such a heavy-duty little tool.
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I honestly don't know if D & M sold any other sizes of the 1/8 HP engine. It's certainly possible. After I built the 1/8 HP engine, I shifted my focus to IC engines, and lost track of D & M. In any event, your engine is an impressive specimen in its own right, and could be made into something really special.
Paula