340 Nodular or 318 steel crankshaft

The steel crank MAY be easier to balance and would be internally balanced as well. Easier to find a neutral balance flywheel.

If you already have the balancer and flywheel for the external balance 340 cast crank, run that. The cast cranks are pretty tough.

IMO, street beater, run the the most cost effective unit you can put together. A 400hp 340 doesn't NEED a forged crank.