Oil pump replacement
You can go to the parts store and purchase an impact driver for about ten bucks, it is a valuable tool to have when something is hard to break free.
It is powered by the blow of a hammer, as soon as you see it you will know what to do, and they have instructions with them. Your basket nut should be righty tighty, lefty loosey, so loosen it by turning left. What I usually do to hold gears in place if I don't have the room for holders is to put a copper penny in the gear mesh (careful, don't drop it inside the engine) to hold them steady. Pennies are soft, and won't damage the gears...then put one in the other side of the gear mesh to tighten..