Since it is so close to the big weekend it might be a little hard to get in to a boat shop right now, So you might need to brake out the tools and try it your self would be my guess. It's normaly easyr to take off the pump off the engine block and do it out side of the boat. Try to find all the old parts of the impeller, Shake out the hose that goes to from the pump to the engine looking for old parts and if you can't find all of them then you will need to trace the hoses around the engine and try to back flush the system till you see the water coming back out the hose you took off the impeller housing and let it drain out the bilge drain plug with the bow as hi as you can go. It's normaly around a 2-3 hr job till you get used to it. is there a lot of room in that area of your boat?