See if you can get a casting number off it.
Some of those Marine Blocks in the Gn iv were BowTies and would go to a big bore of 4.560. They did have a BowTie on the side though.
To tell the trith I have never seen a 454 that would not overbore by .100. I have seen some though that a .125 bore was too big.
Maybe if you are hitting it with nitrous, the .100 over would be too much. I know that normal aspirated the 477 cu in was pretty well done a lot.
Ed