need a matching 1920 carb for my manifold

No, those are casting numbers. The ones you need to I.D. the carb are stamped in it. The early carb (the one one the right in your photo) has the numbers on top between the fuel inlet and the bowl vent. The carb on the left has the number stamped into the verticle surface below the bowl vent valve. I have some later 1920 carbs too if you would rather go that route.