A.G.Mason was a reseller, a lot of the machines they sold were made by White, but not all. I'd say it's not going to be a unicorn, but a badged machine made by one of the major players, most likely White, National or Standard, and also Davis if it's an earlier machine. I've found the easiest way to see what it is, is by the attachments that fit, as those were rather unique to the manufacturer. Top tension machines are also easier to identify because of the tension. The other part that can help identify is the needle plate, which isn't visible in your picture.
That the name is worn off is also a bit clue it's a badged machine. The companies would make them with no name, and that would get added based on what the reseller wanted to call them. Since it was added after the paint process, it wore off easily.
Upon looking closer, it sort of looks like the end of the name might be 'QUEEN' and in looking at the table, that also looks like a White cabinet. I had a New England Queen that was sold by AG White, but right now all my vintage sewing stuff is in a storage container near Atlanta - and I'm still up in South Dakota!