It is a fact that Lee Oswald was in the 1st Floor lunchroom at 12:27. Therefore, it's highly unlikely ( Impossible) that he could have been on the sixth floor and shooting that carcano out of the window.
I'm sorry that this fact renders your theories impossible.....
Could you cite where anyone said they went by the domino room at 12:27? Jarman, I think, said something like "It was 12:25 or 12:28". Is that your source?
The people recording Oswald's claims said he was in the domino room when either two man walked through, or the two men sat down and had lunch there. Jarman and Norman, and I believe Oswald would have known this, would have to go through the domino room to get to where they routinely stored their lunches. Neither men saw Oswald while eating their lunch, so likely Oswald had no idea that the two men had already eaten.
When Jarman and Norman showed up under Oswald's open window on the sixth floor, Oswald wrongly assumed they had just come from the domino room having just gotten and eaten their lunches. Just another lie among the dozens of lies Oswald told officials.