hi TDH !
I apologize in advance if i make a mistake. I found accidentaly some pictures of drum an clip-on microphones of which the shape is pretty close to the beacon's one. I post some pics below (but it's recent models) so you can say to me if there's a chance that this idea is a good one.
On all you can see the little opening which exist on the beacon
For the stabilizer, i believe that it's the micro holder. I found an pic in google but lost it.
I will continue my research but perhaps if any member know a specialist who had worked in 80's years, he can recognize the brand and model.
EDIT --- I just find the picture of the stand :