There is nothing wrong with running automotive plugs in a marine engine as long as they are the correct plug. Marine spark plugs are pretty much the same except some brands of the marine plugs have an SS coating to prevent corrosion.
You stock plugs should be an AC MR43T. They are the same as an R43T except for the SS plating. Also the same an AC Rapid Fire #1 which has an SS coating.
There is a lot more selection for automotive plugs as well.