If the pin is stock (aluminum), try some pentrating oil (Liquid Wrench) and let it sit overnight before whacking it with a hammer. Use a 1/4 steel punch so that you're just hitting the pin and not the casting.

Get the castings off the boat (unscrew the gudgeons; saw through the pin where it goes through the deck with a hacksaw blade) and put them on a work bench to do this. They are much easier to control and you won't be stressing your gudgeon bolts either.