best way to do it would be to set all the carbs w/ the gauge pictured . check them w/ my method, if you like, after that. if they are all the same, don't touch. if they differ, try to match to the one that you think is the most correct one.
someone else might chime in where they think the level is supposed to land in relation to the outside of the carb bowl... but, that differs for most different bikes.
many shop manuals suggest the method i describe and will actually give the specific location it should be at... not sohc4 stuff though, i don't think.