Balanced Crankshaft (Need Help !!!)

Gentlemen and Ladies,

I just got off the phone with the machine shop that balanced my rotating assembly. I took my 1973 340 cast crankshaft in along with the counterweighted flexplate (B&M style) and harmonic balancer with counter weight (Professional Products balancer).

He balanced the crankshaft and said that I did not need the counterweighted flex plate because the crank was internally balanced. I proceeded to ask him how a '73 cast 340 crank could be internally balanced. He said that he looked up the number for the crank and found his book said it was internally balanced. My question is, should I be a little suspicous of this or is it possible that I do have an internally balanced crank? If it is internally balanced, why did it come with the "cast crank only" balancer on the front of the engine?

Confused as always, so any help would be great.