Actually, the driver said Oswald cupped the package between his palm and his armpit, therefore it was impossible for it to be the gun.
The sixth floor was in upheaval; workers were preparing to re-enforce the floor surface with plywood, and had opened up floor space by shifting boxes from along the west wall towards the east wall.
Yep, the building was owned by D.H. Byrd, an LBJ pal. They just happened to be redoing the floor up there during the assassination. A convenient excuse to have strangers running around the building that day setting up nests. Meanwhile Byrd was on a two-month trip to Africa. He would've stayed I'm sure had their plot been exposed (South Africa had no extradition policy). After two months he decided their little scheme had worked and returned. Plus, Byrd invested heavily in defense companies before leaving even though Kennedy had been planning to reduce involvement in Vietnam.