When I took the engine apart as I was told "It's been Overhauled"... It actually was. New pistons, rod & main bearings. What threw me knowing 73 340 is supposed to have a cast crank, the ballencer looked like steel crank balancer so I pulled it , checked the part number in the G Govei books and the part number came up as 1975 only cast crank 318...the rubber was cracked so I ditched that balancer and bought one that you can add the correct weights for that spacific crank. I did check the crank number and is 73 340 only. No obvious balancing marks on the crank. As I stated I bought it as a project and just trying to make sure I don't end up with vibration. Flex plate is a standard small block flex...I'll try to attach some pictures.