ABSOLUTELY ON TARGET! Mr. X

OP, If you strip the paint off you may see the damper is marked "for 360 use only" Maybe I'm imagining things.

Anyway the 405P is a Sealed Power stock replacement piston and no rebalancing is needed. I for one would never try to internally balance a 360 unless either:
1. I owned stock in Mallory Corp, or,
2. I had replaced both pistons and rods with parts that weighed significantly less than stock.

This one is a no-brainer.

R.

PS: The 5.0 ford engine has about 3 times the external imbalance compared to the 360 and they manage to run pretty well.