I can give you my address if you want to get rid of it… .
My antenna is 5 cm away from my autopilot and 10 cm from all the rest of the electronics. It is working without any problems (not one missing time mark in >25,000 images) eventhough the signal to noise ratio might be better if I would move it further away.
I would get rid of the electronic garbage in your plane and just use the things absolutely necessary for mapping. Get high quality BECs. Try to use a optoisolater between the camera and the flight controller.
Or use the flightcontroller to get the timemark and use something like my Timemark time machine: a script to manipulate events within RINEX 3.xx files to get the image positions during post processing.
Or use your Arduino and an optocopler in between the camera and REACH. I guess that should work and is very cheap.