Hi Alex,
You have presented your case with good reasons as far as I can understand the matter.
I think I can answer the question at the end of your post.
If a modern square or rectangular building was supposed to be aligned to north, south, east and west, then an error of half a degree would be regarded as trivial.
Khufu's successor, Djedfre, may have been quite happy for the ceremonial determination of the orientation to have been performed in a traditional manner, so less precise than the very precise alignment required by his father which may have been pursuant to a representation of a celestial mystery or mysteries.
Khufu's pyramid was made to such an exacting standard that it is not surprising that astronomical alignments have been proposed since 1840. Khafre's pyramid could have been aligned to Khufu's pyramid. Djedfre did not have such a simple opportunity having chosen to build elsewhere. It would certainly have been easier for Khafre to align his pyramid to Khufu's pyramid than to the pole of the night sky.
Djedfre chose to honour his father at Giza from an inscription in the boat pit. The rope from Khufu's funerary boat was made from short-lived plant material so it is likely that the plants from which the rope was made were grown at the end of Khufu's reign.
The Oxford radiocarbon study used samples from museums, so this sample would have been an ideal to choice to date the end of Khufu's reign. Was it one of the samples?
In 1970 it was reported that the haifa grass rope from Khufu's funerary boat had a radiocarbon date of 2150 BC plus or minus 105 years assuming a half-life of 5750 years, but after a (stuiver-suess?) correction a date of 2536 BC plus or minus 105 years, as published on page 16 of Phil. Trans. Roy. Soc. Lond. A. 269, with the article on pages 11 to 18 (according to my hand written notes of an article not in my possession having referred to a hard bound copy of the journal.)
Nowadays modern instruments only need a small fraction of the material that was required in 1970, so you could approach the British Museum and ask if they would be willing to release a small sample for radiocarbon dating from two independent radiocarbon laboratories at your expense if the sample has not been re-assessed in the last 20 years. The sample was given the British Museum Code 332 from my notes.
Perhaps you might want to consider becoming a patron of the British Museum if you decided that this sample would be worth investigating.
The date for the foundation of the Great Pyramid was probably around 30 years earlier than the date when the plants were grown. Khufu's reign appears as 23 years in some chronologies, but now thought to be at least 27 years:
In the remote western western desert, south west of Dakhla, Carlo Bergmann discovered inscriptions on a flat topped limestone cone 20 metres high, as published in Egyptian Archaeology No 23 Autumn 2003. The longest description states that it was the Khufu, who ordered two 'Overseer of Recruits' Iymery and Beby, to lead an expedition of 400 men into this desert district:
Quote
Of great historical interest is the dating of the expedition to 'the year after the thirteenth time of counting the cattle', i.e., regnal year 27 of Khufu, which extends the generally accepted length of his reign by four years.'
End of quote
Mark