383 harmonic damper

If your crank is indeed cast, the part number is 3462922 and balancer part number is 3577180. Behind the distributor there is 2 inch square area of the block that will be stamped G 383 if it is a 71 383. These engines were a low performance 383, sometimes with a 2bbl carb, before they were replaced by the 400 late the same year. If you are going to soup this puppy up I would recommend forged crank, correct dampener and since there are probably thousands of these things about they can be gotten for cheap.