I have never internally balanced a cast 340 crank...Have done several 360 cranks...even with scat rods and light weight piston they took a couple slugs of mallory....dont see a 340 being any different
The shorter stroke on the 340's makes a difference.. And the taller 340 stock pistons are a lot heavier than the 360's sp a lot more weight is saved on the 340's.
Thanks on the 360 internal balance....ever consider drilling weight out of the journals, like on the stock 340 steel cranks? (post #6.)