I’ve bought lots of motors over the years and I’m not sure I have ever seen a steel crank with no hole at all. The steel shafts I have in my possession all have some kind of a hole, even if it is too small. I’ve even got some steel shafts out of trucks with pilot bushing installed but they had an auto from the factory. I have seen lots of cast cranks with no holes. That being said, never say never with Ma Mopar. If you have a round aftermarket flex plate with the round notch for the imbalance, you don’t need a converter with the imbalance as well. The three weights are probably just for the initial balance of the converter. I’ve got a picture on my phone of the big oem weight for a cast crank 440 I’ll post. I thinks it’s like 13 oz. My bud just bought a 69 charger 4 speed car. They had installed a cast crank motor with external balance and a neutral flywheel. It vibrated starting at 2000 rpm. There is no way to be sure in this situation until you look at the crank. Do you have a windage tray installed? It may be hard to see without pulling the pan. Someone could have taken a cast crank and had it internally balanced. Look for non factory holes or heavy metal in the crank throws. Honestly, you are just guessing unless you pull the pan. My best guess is that you have a externally balanced cast crank, a flex plate with the proper external balance already on and a neural converter. All this would match. If that is the case,the neutral balancer on the front needs to be changed to an external one to balance everything.