Handles now made, to Gary's measurements, using 10mm B&Q ali tube with screw/rawlplug line attachments a la SiS Bob, wound with tape to fit the 15mm I/D fishing rod handles; and pigtail cords according to Brian's measurements.
Just been to try them out up on Wye Downs for a couple of hours in 10-gusting->15-mph winds. Certainly far more responsive than the original handles but , boy, do my wrists and fingers ache from the gusts. Probably not the best wind to learn to quad- fly in, but still thoroughly enjoyable.
Thanks, all, for your input!