Carb identification help

Thank you for the, gentleman or gentlewomen. I appreciate it. May I ask how you knew it may be the 400? I'm just curious in case I run into a similar situation.

I also have checked the bolt pattern on the manifold and it mounts fine. Thank you for the advice though. It would not have been fun to rebuild the carb only to have it not fit the manifold.

I have not check Mike's Carburetors yet, but I will. Thank you.