Wander out to your particular 135 and gaze up at the Overhead Panel. Observe carefully. All will be revealed. CB's on the SHED BUS 1 and SHED BUS 2 will tell you what is what.
Also take note of AVIONIC SHED BUS 1 and AVIONIC SHED BUS 2 - items listed there will be avionics that get shed and will vary amongst serial numbers and roles as you imply...
Just a small thought, not always do modification centers get the overlays completely nor correctly updated after a modification, or at least on this side of the pond. Not trying to throw mud, or confuse the issue, just something I have noted over the years.