67' 318 crank in a 69' 340

whitepunkonnitro said
Swap in the crank and rods from the 318, and don't concern yourself with balancing the thing.
Yes, there is a weight difference with the pistons, but because it is located so far from the rotating assembly it will not effect anything

^^^^^^^^^^^ THIS^^^^^^^^^^^^

And..... Cast cranks are really tough. I know a guy that spun one 7200 rpm's in a stock eliminator (3.31 stroke factory cast).