I think this 2638 BC date is a dead end. It does not fit the epoch of Khufu's or Khafre's life.
You can see below how the air shafts were designed at a date that matches the reign of Khafre:
Your constellational analysis is valid, but it simply points to a general time of the year. What is needed to pinpoint the specific year and date it observational data of the Sun, the Moon and the planets. We need to take into account all the information that is given to us. This includes the shafts, the causeways, the orientation of the pyramids, as also what is encoded in the Westcar papyrus. The information of the calendar(Peret season etc) needs to be decoded correctly. Also, the distance of specific planets that is encoded needs to be used. This does not fit with the 2638 BC year. At this year also the planets Mercury and Venus are too close to the Sun, thus they rise too early to be easily noticed. These planets are internal are never far from the Sun.
The only thing I find interesting about this year is an rough alignment of 3 planets with the distance ratio of the three Giza pyramids, but this is not enough to earn greater attention. You were closer to the solution in your previous date(not far from ~ 2580 BC), but you need to abstain from using the Moon Gemini alignment as a given. It does not work.