Does anybody know what are the brand and model of the following pictured swivels?

At the top of the �cylinder� is a button that when pushed releases detent ball bearings, and the sling half separates from the base bolted or screwed to the stock. An early "quick release" design. I believe these are 1920 -1940 vintage swivels. (In the butt stock picture, the swivel is missing the metal sling loop.)

Second question: when Savage catalogs listed third party add-on options (swivels, sights, mount, etc.) from the same time period, has anyone received a factory letter for a rifle that specifically names the addition?

Randy, they look alot like uncle mikes but others still make them so its hard to say what brand yours are. I have a set on my F but they are drilled and set deeper into the wood.
uncle mikes push button quick release

Sorry. Now I see; still current. I have seen a lot of Uncle Mike's products on the shelf, just not those. The ones I have are the same as those in your link, except for the "ridges" on the bottom of the barrel.

I dont see them much and dont like them. They are noisy, so I take the sling off the gun when hunting.