Dear Mr Tiny Organ.... Are you aware that Mr "Smith" provided me with the information that Lee hid the paper sack that contained the disassembled rifle and then retrieved that sack with the rifle in it just before he shot JFK?
Where does any LNer say Oswald started for the 6th floor at 12:27?
If you have a problem with Mr "Smith's" statement then perhaps you can present a different scenario. But you need to keep in mind that the rifle could not have been assembled in less than five minutes .....so if you believe that Lee assembled the rifle while other workers were moving about then he would have run the risk of being caught with the rifle.
I think it's possible Oswald took the rifle to work without disassembling it. An inch or two of the barrel end sticking out, easily concealed by holding the bag at the top and tucking the open end in between Frazier's back seat and seat back.
As for Oswald being too stupid or naive to figure out a way to assembly/unpackaged the rifle and place it somewhere without being noticed, is this one of those "superpowers" he would have required?