No magnetometer interference from the ELT antenna or the seatbelt attach hardware.
My ADAHRS (a Garmin GSU 73) is mounted behind the instrument panel. I preferred that location to keep all of my "pitot-static" instruments in one area (ADAHRS, backup PFD, and autopilot control head) to simplify the tubing runs.
I put my transponder in the tailcone to keep the antenna lead the right length. My transponder antenna is back there because I've made provision for a cargo pod and that complicated transponder antenna placement forward--everything's a compromise.
These are the only pics of the VOR doubler I have here at work. The doubler is tied into the aft side of the F-1010 frame.