Hi Mark ... so you are proposing

Petrie determined the mean side length of the base as 8474.9 inches (215.262 metres), so if the intended length was 410 cubits, then the apparent length of cubit is 20.67 inches (525.0 millimetres), which is very close indeed to the apparent length of 20.65 inches from the chamber

In my opinion the cubit was 20.62 for The Great Pyramid AND The Pyramid of Khafre. 411 cubits at 20.62 is 8474.82 inches so I have no idea what tangent you are off on to get 20.67 HOWEVER if you look at The Pyramid of Medium you will find the the cubit that works best there is 20.67488. Petrie calls the height as 3618 inches and this divided by 20.62 gives us 175.46 cubits but if we divided by 20.67488 we get 175.00 cubits even and the base works out to 275 x 20.67488 and we get 5685.6 inches which precisely defines the base of Meidum. And to broaden your scope even further you could bring in The Kaaba, Islam's most sacred object whose size was apparently dictated to Mohammad by God which also when calculated in inches to cubit ratio precisely equals 20.67488. And since G1 and G2 are in the exact ratio of sq rt of 3 to Phi your new value of 410 cubits can only be correct if you call The Great Pyramid 438.89 cubits

db

"There is nothing as impenetrable as a closed mind"
and ..." if everything is a coincidence what is the point of studying or measuring or analyzing anything ?" db