We extend to you a cordial "WELCOME ABOARD !" Come on in, make yourself at home, we are a friendly group of enthusiasts, and we also appreciate the classic Chris Craft Roamer, Corsair, and Lancer boats too , as they are all on the same family tree and share much in common ! Just start by posting a note introducing yourself to the group, that's all it takes here (we don't ask for or retain any personal information here, because our intention is to just "have fun and share information".
The original Carter AFB on the Chris-Craft 427 was a 625 cfm unit, and the Edelbrock 600 cfm marine #1409 is a viable replacement. I've done the calculations many times and the compression ratio of a marine 427 along with our rpm range, which is generally in the 4,000 range and maybe 4,500 for a runabout just won't warrant anything as big as a 750.
Glad you got the issue resolved, but in the past I had issues with cross sparking with the crappy ignition systems they installed on boats "back then" which may have been a result of a bad ground, or perhaps moisture coming up from the oil sump into the body of the distributor, or whatever, but the issue was solved with a DUI HEI-style marine igniton. It's amazing what 50,000 volts will do for you. As I recall you already dealt with that with an aftermarket ignition system.