The three odd float bowls are off carbs that had an accelerator pump fitted.
The forth matching bowl would have had the pump on and would have been on number two carb.
These carbs are either accel pump carbs with the pump missing or none pumper carbs with three odd bowls.
The pumper carbs will have a jet sticking up in the mouths of the carbs which i can't see from this angle.
The brass tubes on the bowls link together to feed fuel to each carb accel jet.
If these are std carbs and you have no spare std bowls then just switch the middle two bowls and connect them all up with some tube to blank them off.