The correct balancer for a cast crank 340 says "For use with cast crank 340 only" on it IIRC. Regardless - if it has a balancer that is for a 360, it has some kind of offseeting weight - which means it's externally balanced and will need the external balanced flexplate too. Question is - which one? Can you get a part number or clear picture of the balancer?

Well, art is art, isn't it? Still, on the other hand, water is water! And east is east and west is west and if you take cranberries and stew them like applesauce they taste much more like prunes than rhubarb does. Now, uh... Now you tell me what you know.