If those non-us made cast cranks for ford can take over 500hp with out cracking don’t you think a cast Chevy crank could take more? Think about it. Secondly rectangle and oval port big block Chevy factory casting are able to make well over 500 or 600hp that’s a fact. The ports are not too large and very different from 4bbl Cleveland heads. I say go for it you’ll be way ahead of the 460. You already have the forged crank and 4 bold mains. Ever price a forged 460 cranks or block with 4 bolt mains? Go for it and good luck