Measuring the circumference of the earth - revisited
You can use the fact that the Earth's rotation period is known.  Then divide that period (use the solar day of 24 hrs 00 minutes instead of the sidereal day of 23 hrs 56 minutes) by the actual amount of time between your two solar noons and multiply the resulting factor by your 1260 km distance.
The result is the circumference ... of your latitude circle.  To get the circumference of a great circle and thus the Earth, you need to divide the calculated number above by the cosine of your latitude.  To get the latitude perform your experiment on an equinox and measure the shadow angle at solar noon.
Have fun, good luck!