’73 440 HP-forged crank, HD rods, and ’73 low compression pistons equals full internal balance, no counter weighted damper or flywheel/TQ. Only the ’70-71, a few ‘72s, high compression piston/HD rod combination (six-pack motors) had external balancing with a forged crank originally.

1972 Road Runner GTX 440 6bbl 5-speed
[img]http://72rrgtx.com/carpics/bucket/DSC06730r-1.jpg[/img]