Internal or External Balanced Harmonic Damper?

If someone could please help, I pulled this harmonic damper this morning to replace it, I am not sure if I need to buy an internal or external balanced damper? I am working on a 1972 Plymouth Scamp. The vehicle originally came with a 318, it now has a 360. If I did my research correctly the 360 engine is from 1976. I read in one of the forums that all 360's are external balanced. I do not know anything about the original engine build. I don't want to put on the incorrect balancer and damage the engine.. I have a 727 three speed automatic transmission, not sure if that info matters. Any help would be great.

Balancer back side.jpg

Balancer Front Side.jpg