360 build.

Jadaharabi said
The 360 flywheel is balanced for 360s only.
68-71. 340 are internal balanced engines and the 72-73 are external balanced.
The 340 external balance flywheels are not balanced for a 360.

The 72 340 was also internal balanced as it was the last year for the steel crank. Only the 73 340 was cast and externally balanced.