That oversea's produced CMB Carb that has the 3rd channel built in is a bit bulky. I would suggest getting either a MARK BULLARD Carb or a OS Carb.
The stock carb from CMB that is sold on engines in the US is solid carb as well. You will need to look at several other factors that may help you decide. What elevation, what boat are you running it in etc.. The bore of the carb can drastically change the performance of your engine.