I agree with Stephen that the generally a cubit is one and a half times the foot in any given ancient measurement system and I do not see why that should not be applied to the ancient Egyptian measurement system as well.
I am not sure it is fair to say that there is no evidence of an Egyptian foot that is 2/3 the length of the Egyptian cubit, since most of the dimensions that are an even number of cubits are also an even number of feet. For instance the GP outer dimensions of 440/280 cubits are 660/420 feet. Or the dimensions of the KC are 10/20 cubits or 15/30 feet, etc, etc.
However, one measure that makes more sense in feet than cubits is the equatorial diameter of the earth. It is 24350000 cubits which is 36524000 feet, a pretty recognizable number:
Equatorial circumference = 24901 miles
24901 divided by pi = 7926.2345 miles (equatorial diameter)
7926.2345 x 5280 = 41850518 English feet
41850518 x 12 = 502206216 English inches
502206216 divided by 20.625 = 24349392 ancient Egyptian cubits
24349392 x 3/2 = 36524088 ancient Egyptian feet