I'll tell you why I am less impressed about the brother/sister package length assertions than I once was.
They were motivated to agree before their 302s were taken to discuss and synch their stated approximations of the length.
LInnie Frazier Randall estimates package length to FBI on 01 Dec., 1963:
https://www.maryferrell.org/showDoc.html?docId=1140&search=linnie_and+package#relPageId=426&tab=page
Possibly they had a day's advantage to satisfy themselves (a reliable assumption, or not) there was no reporting of other witnesses claiming to have observed any similar paper sack while in transit. Frazier had been subjected to harsh interrogation including psychological manipulation. Police searched their home and
confiscated his rifle, of US manufacture.
Frazier and his sister had no incentive to admit observing Frazier transporting Oswald and a paper sack actually a foot longer to the TSBD and Oswald infamy.
They were country people from Huntsville, Frazier only months before. Is it unreasonable to contemplate they were suddenly deer in the headlights, their 27" assertions a leap away from the headlights's beam and of the path of the course they illuminated?
Your Ferrell link re bag length has revealed a few details of which I was heretofore unaware. Namely that Buell saw only a 9"X1" section of the bag as viewed from behind while in Oswald's palm/armpit.
I have been looking for information that would confirm that Buell, at any time, saw Oswald with the package fully revealed to Buell in a full-frontal perspective. Additionally, no one has been able to confirm that Oswald's free arm was in full view as he walked ahead of Buell.
I have experimented with a 35" long-heavy object that can be supported by the left hand, and by drawing it across the chest, (while still supported in the palm in the other hand) can, arguably) be carried out of the view of a trailing, distracted trainspotter.
(The Ferrell link informs that Buell estimated Oswald was no closer than 12' feet to him on the walk towards the TSBD that day)
In addition, I'm 6'-6'1" and can only get 22-23" jammed into my armpit and held in my palm. A 5'9" man would have to be a real knuckle-dragger to get a 27-incher to fit.
Finally, do you know how much the curtain rods weighed?