Quote ' with a cubit of 528mm G3 would have a base of 200 cubits'
If your working on Petrie's base length you are correct. You know I have taken Edwards base 356.5 (356.4) 10 feet almost difference. I believe Petrie was not able to get a good base measure for the simple reason to much sand build. He writes p.37 "at this level then the sides averaged then 4153.6' I may be wrong here but I have chosen to take Edwards as he had plenty of time to correct his mistake but did not do so.
Here to me is the problem everyone is going for cubits as the exact measure and 200 is very reasonable but look.
356.4 feet = 4276.8 inches and in Northern/Saxon/Indus feet 13.2 the base =
324 feet perimeter 1296 feet and to convert to royal cubits and ordinary cubits find digits and there are 16 in a foot so 324 x 16 = 5,184 digits the same number as the slant height of the GP.
I think the royal cubit is 20.625 inches and is = to 25 digits.
Base royal cubits 207.36 royal cubits. Many people would look at this and say 'I don't think so'.
However this number or 1/2 ie 103.68 was recorded by Flinders Petrie in the second pyramid when measuring the coffer in G2. P.36 "outside, length 103.68' and in imperial feet this is 8.64 feet exactly.
Now back to the 3rd pyramid and a base of 324 Indus feet an ordinary cubit is one and a half feet or 24 digits.
5184 / 24 = 216 ordinary cubits giving perimeter 864.
These people had the numbers down pat.