I am trying to find the correct maximum total advance of my merc 502 mags so I can choose the right ignition modules

Well if it is a stock carb we would have set the timing at [36 btdc] at 3200 rpm

Do you have modules and need to know the advance on them??? or you are looking for the best modules for your engines????

Factory full advance was set at 32*, but you can easily go 34*. The rpm for full advance varies between 3000 and 5250rpms depending on which module you have.