Many thanks to Willie Morgan and his wife Megan, who make costume jewellery and know about glues. By the way, I think Megan Morgan is an excellent name.
This is the stuff. Evo-Stik Serious Glue. Leaves the tube with a jelly-like consistency, does not tend to string or run about. Stays moveable for 3 minutes, sets hard in 2 hours. Fully cured the next day. It will fill gaps, stick uneven surfaces.
I haven't done all the beads yet, but am working through them. Fiddly fiddly. This requires some care, since the little magnets will happily leap 4 or 5 inches to join a neighbour, or stick to my penknife. You need plastic tweezers for this job. Here you see a couple of finished markers on the laminated master map - a division of the Armee de Portugal in Valladolid, plus a garrison in Burgos castle to keep the supply road open.