DF-31A: 39.803634° 116.710562° (11.8.09); 39.800048° 116.709524° (23.6.09); 40.145280° 116.121080° (29.8.15);
I've tried to calculate the dimensions of the missile containers using this image. Of course, resolution is low so some figures aren't precise. Especially width of containers. (I am getting 9 pixels for JL2, 10 pixels for DF31AG and 11 pixels for DF41) So measurements may easily be off by a few decimeters or even close to half a meter.
Anyway, my measurements are these:
JL2: 12.5 by 2.5 meters
DF-31AG: 15.5 by 2.8 meters
DF-41: 18.5 by 3.1 meters
DF-26 missile length (not container) 16 m
I really wish I had satellite images of DF-31 and DF-31A for comparison, as well. Sadly, I don't. Unless someone can help me out and provide GE coordinates or something...
DF-31: 36.824866° 101.106507° (27.6.11); 36.828577° 101.109517° (27.6.11); 36.948611° 101.666244° (6.6.11)