He didn't just say that he saw chicken bones on the fifth floor. He said that the sack containing those chicken bones and the Dr. Pepper bottle, that he filmed Studebaker dusting for prints, were on the fifth floor and that there were no chicken bones at all on the sixth floor.
Alyea's film footage doesn't prove what you think it proves.
The chicken stuff that was in the Smoker's Nook behind the SE corner window on the sixth floor apparently was moved around a bit before it was gathered up to be taken to the DPD crime lab. Perhaps it had been removed or moved to a different location and it wasn't there when Alyea saw the Smoker's nook.... Neither you nor I can know the exact details....
And Alyea's footage most certainly DOES show the Carcano lying on THE FLOOR on it's right side, with the butt plate parallel with the floor, and on a North South axis. The leather sling was up......
That rifle was NOT jammed between boxes of books when Day picked it up by the leather sling that was right there at his finger tips...