Could I use an air/fuel ratio monitor on the 12A to tune the carb like a piston or not?

 

Um, probably. Most Narrow band O2 sensors are crap though, and not really useful for tuning anything. Since you're NA though you can't really hurt the engine, and it will at least give you some idea, which is better than stabbing in the dark. I'd recommend a WB still. They're much more accurate, and can help you get the tune spot on.