So maybe he's being set up not as sixth-floor gunman but as having owned & supplied rifle used.
Yes, I can go with that. As I've always thought, the conspirators had their plan and the authorities had theirs (the depiction/use of Oswald as the gunman).
If Oswald supplied the rifle he'd ordered, he musn't have known that the shooting was programmed for November 22nd. He might even have lent the rifle to a friend/contact with no notion that it would be used as an assassination weapon.
And if, as you believe, a Mauser was found on the sixth floor, how would this be part of a plot to frame Mr Oswald as the Lone Nut sixth-floor shooter?
I'm remembering old threads saying that it was a Mauser that had been found initially (described as such by officers). Then there was the notion that the MC was substited before Tom Aylea arrived on the scene to film the extraction. I've been away from the forum for a few years, so all that might have been eliminated as a possibility.