I know the BBC guys run 454 cast cranks to 500hp all day with no issues at all (even the stock car guys) So I'm assuming you could safely do something similar with a 440RB.
I would look into having the cast crank and recip assembly internally balenced. I've hear of it being done. however you may have as much Money in it as a forged unit will cost you.
If you want to extrernally balence it Moparlover is spot on.
