B&M flex plate

Now that that is all cleared up, I hope Byron doesn’t mind if I swerve his thread a bit.
Can someone explain WHY they made the 360s external balance? If all 318/5.2 were internal balance, why the need to inventory different harmonic dampers, flywheels, torque converters and/or flexplates? It would seem only having 2 different cranks would make for less chance of mistake as well. Wouldn’t an internally balanced engine be smoother running overall as well?