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Do you know it is Oldsmobile? Looks to me like a straight eight assembly with that husky ring and B series belt, possibly Oldsmobile but Pontiac and Buick also look very close in appearance.
Most everything so far has ended up being Olds but it could be other GM brands. I would think there would be some ID but I've looked it over nine ways and can't find a mark.
Apologies for the delay, it appears very similar to the combo on my '40 257 straight eight... Mine appears to have an "8" stamped in the side, does yours have a number?