It seems likely now that SteinAir forgot to include the assembling kit(s) for the backplates on at least the Garmin remote transponder. The backplate was tossed in a big but there should have been screws for the connectors. I searched everywhere and found none but at least I sorted out a bunch of hardware bags into the appropriate trays while waiting for the last camper rental of the season to return.
A person on Facebook is going to send me the screws so I can move forward. Had some communication with SteinAir but it was a Friday afternoon and I don't know what the resolution will be if any. What other kits need to be ordered? No clue.