I put it aside as a winter project, and it's now winter. The gun needs disassembly and a good cleaning, a few metal parts need a bit of re-bluing, and the wooden stock and pump would benefit from re-finishing. There was no factory instruction manual; I found one in Remington's website and printed it. The case was old and disintegrating so I went to Cabela's and bought a new one, plus some gun cleaning supplies and a tool kit.
Since I'm a visual learner I thought I'd see if there were YouTube videos for disassembly. And I found this video of a man having a heckuva fun time shooting bottles, gongs, cans, zombies and other things with his Remington 870. Zip past the one-minute mention of an eBay sale at about 2:00, and enjoy the rest of the video. I'd like to be on his property!
The guy is a pretty good marksman - hitting a gong at about 100 yards with a shotgun slug is not an easy thing to do.
When I have finished reconditioning my father's shotgun, I'll keep it next to a 1917 Stevens 10 gauge that I inherited from my grandfather a few years back. That gun was given to him by his father (my great-grandfather) when my grandfather was 12, because his job was to go into the woods and not come home without meat for supper. While neither gun is especially valuable, they are filled with priceless memories.
Enjoy the video.