Harmonic balancer help

It'll be interesting to hear what happens, but that doesn't make any sense.

The cast 340 and 360 have different amounts of weight balance.

Here's what the Pro Products balancer says about theirs:

"This damper is supplied as a neutral balance damper and comes with three bolt-in counterweights. This allows this one part number to fit four different small block Chrysler engines. The damper without any weight fits internally balanced 1967 and later 318 V8's standard and Magnum, and all internally balanced 273 and 340 engines with forged cranks. One weight is for 340 externally balanced 1972-’73 engines with a cast crank. A different weight is for 360 externally balanced 1993-’97 engines with a cast crank. And the third weight is for 360 externally balanced 1971-’92 engines with a cast crank. Each counterweight is numbered, and the instructions guide you which weight to use for each style of engine."

Seems fishy to me.