Well, some of the air-cooled models have a separate tag on the block for the manufacturer of the powerhead. For example, I had a 1970's Ted Williams (made by Eska) that had a Tecumseh built powerhead. But, in general, most motors have a serial#/model# plate somewhere on the shaft housing, transom mount, or cowlings.
What color/finish is it? Does it have a built in tank or does it require an external hook-up? These things might help a little, assuming the finish is original.
Thanks-it does need an external tank. I'll check for #'s where you suggested. It has a blue shaft housing and a red color on top---may have been painted by a previous owner. It came from Maryland--My wife's deceased father had it.