Hi Clive,
Your angle for G3 is wrong, the correct angle for G3 is 51d 19m 4.86s close to Lauer's estimate of 51d 20m a product of the geometric construction shown below.
The construction illustrates the Ancients’ design, which is integrated on the Giza Plateau. Stating segment AD produces lines BE, EF, FG, GH, HI, IJ, JB as the approximate1 7 segments of a circle with an angle of 51° 19’ 4.86” or the angle of the Pyramid ofG3. This construction was taken from the Giza Plateau Centered on G1 and the gammon base of the Sphinx as the radius of the circle.
Regards,
Jacob