[Oldsguy]

You are right, I forgot about those marine application carbs. I am going to have to disagree with you about the carburetor cfm rating though, 650 cfm seems a little too small for the 455. You will probably get great throttle response from a smaller carb like that but my experience is that the 455 likes about 750 to 800 cfm. Anyway, even if you end up using that carb, it should work well being a vacumm secondary, espcially with a 600 cfm rating, for the street use.
I still wonder though about the thing flooding the engine, is there fuel gurglining out the vent pipe? Or does it kill the engine and then the thing stinks of excess fuel? It couldn't be a vacumm leak could it? I have a '76 Omega with a chevy 6 cylinder and single barrel carb on it and that thing got a loose baseplate once that was leaning out the engine but it was acting just like a flooding engine. The thing would bog down and almost die during highway driving especially on high throttle situations like merging or passing. I misdiagnosed that for a week until we figured it out. Tightened up the baseplate nuts and the problem vanished! Let us know what your friend finds out ok?