Speculate away, but don't pretend that speculation is fact.
Nice strawman, but there is ZERO evidence that the package seen by Frazier contained a Carcano rifle with serial number C2766. Or any rifle whatsoever.
ZERO.
The testimonial evidence is that, at a minimum, Oswald carried a package that he said contained curtain rods and that was sufficiently long and rigid to cup in his palm and under his armpit. Based on their cursory observations, Frazier and Randle estimated the length at 27-28". Randle also said he was holding it in a way that it almost touched the ground. The negative evidence is that no package of curtain rods was found in the TSBD. Oswald, if we can believe the record, denied having spoken of curtain rods, placing a package in Frazier's car or taking a package into the TSBD (other than his lunch). 27 or 28 inches would indeed be too long (by some 8 inches) for the disassembled Carcano, and the rifle would be too long to cup in a palm and under an armpit. But, of course, the rifle was in fact found in the TSBD. (We could add that David Lifton once insisted he had a witness and her supervisor who heard Oswald say on a TSBD elevator that he was carrying a fishing pole, but we'll let it go.)
So, yes, there is a huge conflict in the testimony and evidence. Obviously, Oswald's otherwise puzzling trip to Ruth Paine's and the fact the rifle was found the next day are highly suggestive. Unless Frazier and Randle were flat-out lying for no apparent reason, Oswald was carrying a long, rigid package. The most plausible explanation, it seems to me, is that Frazier and Randle, despite their strong claims to the contrary, were simply wrong in their estimations of length and that Frazier was incorrect in his observation that the package was tucked under Oswald's armpit.
Yes, we don't know the package contained a rifle - or curtain rods, for that matter. But the scenario is not a complete blank slate, and reasonable inferences can be drawn. Sure, researchers of the quality of Pat Speer believe Oswald was actually carrying curtain rods. Given the totality of what is known, this is not as plausible to me as that he was carrying the disassembled rifle. How likely would it be that he concocted the curtain rod story, and then denied it (presumably because he knew there were no curtain rods), while conspirators were placing his rifle on the 6th floor to frame him? If there were curtain rods, why would he not have told the police where they were in the TSBD? This to me is another area where it's difficult to see how any conspiracy scenario makes any real-world sense.