Well, this morning I finished my paint job, reassembled the 870 and was able to relieve my AR-15 of bedside protection detail! I had decided to go with spray paint after some consideration, as I have access to my buddy's blast booth and the work could all be undone if it didn't turn out well.
Supplies included new (clean) mech's gloves, plenty of acetone and lint-free cloths, and extra-fine scotchbrite, as well as several pairs of powder-free nitrile gloves.
I don't have a "before" photo of the black oxide finish as it currently was at the start; this image was taken after I removed all rust and scruffed up the surface with the above mentioned scotchbrite. Cleaned thoroughly with acetone.
Baked the parts at 210 degrees for a hair under ten minutes to get a nice level of heat into the metal for the first light coat of paint. Allowed to cool slightly. (Cool enough to touch bare skin, though my hands were freshly gloved)
Rustoleum Hammered "Antique Pewter" ($5-something at Lowes) and Krylon Matte Clear (under $4 at Walmart) were used for the job.
Sprayed four light coats of paint in all, allowed ten minutes to set up before each next coat. Allowed a 30-min air cure, then baked the parts in the gas oven for approximately an hour at the same temp. (210 degrees) A shout-out is necessary to my loving wife, who didn't mind me using the oven for a few hours each day. I should also mention, the vapors were not terrible at all. Just kept the fan running on the over-range microwave and lit a candle.
Allowed the parts to cool; then let sit at room temp for 24 hours. Sprayed a generous coat of Matte clear and baked at 190 degrees for a half hour, allowed to cool and sit overnight.
A decent closeup shot of the finish:
I'm very happy with the way it turned out, especially for $10. I believe with the paint having been baked, it will be at least by some margin more durable than a standard air-cure rattlecan job, though only time will tell. This barrel doesn't see nearly as much action as the 28" does; I haven't touched that yet except to remove the two bead sights, I was thinking about doing something with a little metallic blue and red paint I have on hand, in addition to this Rustoleum paint, in the form of an American flag.
Cheers fellas, just wanted to share my experience with everyone!