While you are resealing the engines, consider replacing the rear main seal and the front crank seal in the timing cover. Especially since you plan to reseal the oil pans.
The differences that I have seen in marine grade parts is that they are either sealed, or as in the case of alternators, they have aluminum screening that supposedly absorbs enough heat from a flash to prevent combustion beyond that point. That's how a flame arrestor works.it absorbs heat from a flame...supposedly.
The starter on my engine looked like a car starter. Without knowing the history, I opted to replace it with a marine starter, and it looks different. That is not to say that the one that was on my boat was not marine grade, but I had serious doubts and played it safe. I found them to not be all that expensive.
So I apologize that I cannot tell you what to look for specifically, In my brief experience I have wondered the same thing and found that there are differences. They are not the same parts for more money like I originally thought.
