360 build.

Jadaharabi said
My first 72 Duster 340 was a cast crank and externally balanced and all I've ever seen have been. Although I've been told early 72s might be either way.

If it was a late 72 it may have been a cast crank. I was the second owner of a a very early 72 Demon that had 2.02 valves and 10.5:1 Pistons.