1969 Mercury 20HP scrap yard find

Edit: Oops, posted in wrong spot. I will repost. Hello all. I have been mostly hiding over on the Johnson/Evinrude side of things. But I will now be dabbling into these waters. Today when at the local dump, at the scrap pile was a Mercury 20hp short shaft there. Took it home. It had a mouse condo under the hood to clean out. Drained and refilled the lower unit. New spark plugs. 100 lbs compression in both bores. Also the points were BAD dirty. However they cleaned up nice. Got a nice strong blue spark back and fired right up and purred away in a water tub. However I believe it needs a new water pump impeller for sure, no water from the tell tale, I will make sure that is clear. The tub had plenty of water up to 3 inches from the transom clamp. Other than getting water moving again, anything else to look at or be aware of? Bottom ends pretty straight forward to pull apart? Mercury pump kits look "NLA". I will keep looking, otherwise order separate items. A buddy is looking for something to power his 16 ft Lund fishing boat. Even if we end up putting $200 in parts, it is still a deal for him. From what I have been reading, these seem pretty stout engines.