Is it a steel or aluminum oil pan somewhere right around 73-74 they went to a cast aluminum oil pan. Have the block sonic checked before you put any money in it, most marine engines are freshwater cooled and even in freshwater they get a lot of rust in the water passages in the block, it should have a cast iron intake and a cast iron timing chain cover. Marine engines used the early pre 69 water pump all the way thru 1985 when they stopped producing marine engines.