What's wrong with using the 318 crank that is already in the engine? Even if it's cast, How many broken 318 street-cranks have you ever seen? or heard of?
I was just on the phone BSing with a life long friend and he just brought up a time when he broke a cast crank in a Pontiac Grand Prix way back when.
He is notorious for pounding cars into the grave early.
It’s also one of the reasons he got into and stayed with MoPar.
He used to pound on cars like no tomorrow, but the MoPar kept up with him. (Save the - 383 he had in a ‘69 Road Runner. But that wasn’t a crank issue.)