Dump tube is what the main goes into. On some alky carbs they are drilled out b/c it takes so much alky, that even if you put in a huge main, it would be bigger than the dump tube. I'm not sure how to find it. On some carbs it is replaceable, on some it is not. I think it would be best if you got with the guy you got the carbs from and tried to get all the info from him.
IF you've already listed these sorry, but
Carb size, brand
dump tube size, main size, pilot, needle, etc.