I changed my oil pump O ring in the winter. I took some soft copper wire and looped it around the pump and when I removed the bottom plate I secured the pump gears in place. Set the O ring in place and loosed the wire enough to slide the bottom plate in place
While you are down there and all dirty anyway, remove the big nut next to the oil in tube. Check the spring inside, and make sure the sliding part is free and clean. You may want to add two flat washers under the spring to raise oil pressure.
