The do share the same bore, but not the same stroke. The 283 stroke is 3.00", the 307 is 3.25".
I'll give you a start in your search, the 740P piston was manufactured by Ohio Piston & Pin, now out of business, and sold under the brand names Nytel and Ertel. They were once associated with Dynagear, but not sure in what capacity.
Maybe some here from back in the day can shed more light.