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You referred to a 48 degree azimuth which is the angle by which the calculations were done. Where did you get this number? You use the G1 - G2, that is Alnitak - Alnilam positions to calculate it. But at 2550 or so BC, the azimuth at transit of these stars did not go close to 42 degrees or the complementary 48 degrees. The same thing holds for sunrise and sunset. So Don correctly considered this totally arbitrary.
From my calculations, if you were to take Lehner's values for G3, then reverse engineer based on Petrie's G2 dimensions , then you whould come up with a G1 base of 223.7 meters. This is 6.65 meters or 12.7 royal cubits smaller than the actual size of the GP. The error 2.9%.
So apart from being totally arbitrary this theory yields a very large error when computing the base of G1. It is thus practically useless.