Cast 340 Crank
 

Can you internally balance a 340 cast crank?, they did have weights on the torque converter.

Re: Cast 340 Crank
 

Of course. It's done all the time with externally balanced 360 cast cranks, including mine. Any lighter than OEM weight rods & pistons being used will just reduce the amount of mallory metal, or whatever, that is needed to do the internal balancing.

The OEM 340 cast crank engines also had that special damper/balancer that had "For 340 cast crank only" cast right into the counterweight.