I came up with three posibilities for the casting #, I would assume that it is the second one, however it can be crossrefrenced by getting the casting #'s off of the heads. On a long shot you might just have gold on your hands
Casting #...ci.......year....bolt......type/usage
3970010....302.....69........4........Z-28 Camaro
3970010....327.....69........2........Trucks and industrial
3970010....350.....69-80....2 or 4..Dealer Replacement