I asked this question to a buddy of mine who owns/operates a boat sales and repair center.
Below are some of his comments.
the only thing you can check is the float drop.
you can tell him that the floats should sit parallel to the carb body when "GENTLY" tilted over with the float facing upwards.that will get him as close as possible without the float gauge. the measurement is build in to the float gauge. and the float gauge rests on the outer lip of the carb body and the float must lightly contact it without depressing the needle into the seat beyond the spring mechanism.The gauge is a dealer item.
I hope this info helps---if you need me to ask him anything else---just ask.