Congratulations - great bit of detective work !
The rectangle on the map (strangely truncated by the grid line) presumably marked a wall or fence around the central antenna and hut. I suspect that by 1960 the radio range had been dismantled, leaving only the NDB, but if I'm not mistaken the orientation of the fence/wall matches the orientation of the original radio range beams. The Epsom beams were more-or-less at 90
° to each other (though that wasn't necessarily the case for all radio ranges).
So the original four antennae would have been outside the rectangle, but in line with its vertices. Sadly, no trees planted in the holes.
