The aerial mount you mentioned is actually for the B-Set. Has a squeeze lever to open the opposite end which then holds onto a fuel can or seat back as needed. Very similar to the clamp ground a welding rig has with the black rubber aerial base for the B-Set connected to it.
You can see photos of my jeep when it was in a signals configuration at this page:
http://visualcollector.com/OBLI/JeepSignals.htm
The A-Set aerial is the one on the back of the jeep connected to the live wireless battery rack. Two additional battery holding racks are on the wings. This is a British airborne configuration and not how it would have been done for a normal British or Canadian infantry signals jeep. Just posting the site so you could see the two types of aerial mounts which would have been used across the board.