the original converter is the right size and right bolt pattern, no weights on front but there is strip weight on the side of the converter. came out of 69 318 car. you're saying a 340 converter was neutral balance?
followup, bought the one from jmk i listed on transmission forum, on to next problem. just a little side note here, I had a very hard time getting that rubber hose on from intake to water pump. Just about got engine cleaned, painted and reassembled, will post pic when done.