I think you will find you have an externally balanced cast crank 340. That balancer I don't believe is for an internally balanced engine. The balance holes are pretty deep and also about the same width and length as the scallop taken out of some of the later LA 360 engines. I know those are different, but nonetheless, I believe that's what you will find. Just no way to tell without removing the pan. Did the engine run good and smooth with no vibrations? I am betting it probably did.
