What the heck? Did you drop your boat off a parking garage?
From the size and quantity of cracks, I would suggest finding a donor drive from ebay or any boat scrap yard. These engines are expensive to maintain and thirsty. More are being scrapped. The castings were not great when new. I have only heard of one case of successful welding and that was on the engine block. I have seen entire pumps (no engine) on ebay for $250.