If your pump is scored it is bad, this is true of all oil pumps of this type. There is also a spec on the clearance between the housing and the gears, so if you buy a used pump be sure to check it to find out it is out of spec as well. $500 seems like alot of money, however how much is your next trip worth? Taking the family/friends on a vacation or other important event? When your truck strands you on the side of the road, or worse out in the middle of nowhere, suddenly $500 isn't that much money. Except now that is just the tow bill to get you home, not to mention the entire engine is now only good for anchoring your boat.
You can pull the mains and let the front of the crank hang by the timing chain, just think you will have that much more room to work with since yours is loose.