My mirror is this item 352011822672 with its spring clips attached but it wasnt sold by the same vendor. Your mirror might do the job if you can find the two spring clips that insert either side of the base in the hole that runs through it. Ive never looked but I believe they fit in there and then tightening the two screws in the base adjusts the amount of closure of the clips so retaining the ends of the visor swivel rods more tightly...
sorry not explained that well, its the clip on the top of the rear view mirror stem . (in one of the pics earlier) allows you to disengage/pop the arm out and rotate to the side if needed
1964 1600 Vitesse 6 Cactus and Black , now sold now have T2000 Mk2 saloon in French Blue/grey trim been restored without running since 1997 now has power steering ,poly bushed and Alfa 156 seats location Luton
Sorry for the slow reply, thanks guys! Received my sun-visors from eBay today, sadly bit disappointed, foam disintegrating, very thin, painted surface, very stiff to turn. Guess something to play round with refurbishing.