Glad you enjoyed it. Unfortunately I do not have the GPS feeding position into my EXIF data, but that berg is approximately S69*13' E076* 26', and I was in the other aircraft at 1000' with a 70-300mm lens.
As for the prop sync, yes the aircraft is equipped with prop sync, although it is relatively uncommon in that it is not a master/slave sync. Magnets create an electric current that are fed into a controller that detects phase difference and varies the voltage to the synchronisation unit that then controls the prop governor. You can also turn the knob to pick up the top or bottom of the wave as is quietest.
I presume that they had it on at the time (normal cruise ops) but looking though my photos it is merely coincidence that they are aligned. Of the aerial photos in my files, this one was one of the few that have the props perfectly aligned.
Cheers
CS