I've decided that the tiny little carb that was mounted on the bike wasn't stock. Neither was the intake manifold, which consisted of a bunch of rubber grommets shoved between the carb and the head. So I made up a little manifold that transitions from the round carb opening to the almost square opening on the head. I also made the carb flange to mount to a 20mm Keihin carb I had brand new in the box. I still need to clean up the manifold and make flanges, but I'm thinking this will work.