Flywheel identification

[aumick10]

Help identifying flywheels. I have two sets of late 61" flywheels here. One set has a "B" cast into it and the other set has an "A" cast into it. Both sets have the same casting no "150-24"
Does anybody know what the difference is between them?
The balance holes are in completely different locations so i wonder if they are for different pistons.


Cheers.

[Jerry Wieland]

Difference between cast or alloy pistons. Maybe different casting patterns.