I searched it on a serial number lookup and it is a 1957.
Here is what it said:
Year: 1957
Location: Kalamazoo, MI
Info: Archtop models have a stamp on the inside of the F-hole. On flat tops have a stamp on the neck block.
I do agree that Mick Mars is underrated and not talked about enough. Whenever someone think famous 80 guitarists Mick does not come to mind, whenever people think of Motley Crue they think of Vince, Tommy and Niki but not Mick.
In the the late 80s when everyone was trying to play like Eddie Van Halen or playing really fast it was Slash who brang back the classic rock bluesy sound. But I know what you mean and its cool to see him expand his ability in his new album.