3970010....302.....69....4 bolt mains...Z-28 Camaro
3970010....327.....69....2 bolt mains...Trucks and industrial
3970010....350...69-80...2 or 4 bolt mains

TDB shows as a 307, you will need to give us more specific info on the letter stamping. Clean it off really well with a nylon bristle brush such as a toothbrush and solvent.
.