The issue is not the length of the paper bag - it's the length of the object in the bag.
Both Randle and Frazier report Oswald carrying the package in incredibly specific ways that, if taken at face value, make it impossible for the object in the paper bag to be a rifle, disassembled or not.
Frazier has the object cupped in Oswald's hand and held under his armpit.
Randle seems to describe Oswald carrying the object down by his side, almost touching the ground.
It doesn't matter what guesses Frazier and Randall made about the length of the package.
What matters is the way they describe the object being held as this sets a limit on how long the object can be.
For a man of Oswald's physical stature, it is physically impossible for him to be carrying a 34.8 inch disassembled rifle in the ways described by Frazier and Randle.
At a guess, the object must be somewhere between 24 - 28 inches in order to be carried in the ways Frazier and Randle describe.
If not a rifle, what can this object possibly be, as it is clearly not Oswald's lunch bag?