The rods sticking out the back of the muffler are used to lay the motor down on and the rings on the bottom are for steering hookup. The spark plug covers are to protect the plugs.
I’ve heard that back in the day when they raced opposed twins like this with the spark plugs sticking straight out, a competitor would break them off with the bow of his boat, putting you out of the competition. Moral of the story is, if you go racing, it’s best to leave the covers on!