Documenting spacing requirements and planned location for each antenna:
COM1 - mounted on belly under pilot side rear seat, at least 6' from other COM, no specific requirement from xpndr. measured 42" from planned xpndr location.
COM2 - mounted on top of tail cone - at least 6' from other COM antennas, "as far as practical from ELT" per G3X manual
GPS - minimum of 2' from com antenna. min 3' from COM unit. No closer than 9" to other passive (GPS) antennas. per G3X manual. Some are mounting on top of fiberglass cabin top. Van's says not to drill hole in cabin, need to research.
ELT - didn't find specific spacing requirements. Will mount on tail, just ahead of the rear fairing.
XPDR - mounted on belly under co-pilot seat. Minimum 3' from unit. Not within 3' of ADF OR ANY OTHER COM ANTENNA per GNX375 manual
NAV - In the left wingtip - no issues (Back-up location is top of vertical stabilizer)