AT FREAKIN' LAST!!! After months of hassles ( I got the parts sent from Classic American, and our wonderful British Post Office managed to lose 'em :mad: ) my problem is solved.
Just come back from three weeks vacation with my sister in Ottawa; got the parts I needed from Bill's Truck Shop in Courtice, Ontario (HIGHLY recommended) and I now have two fully functioning stop lights.
One very happy Limey!
Thanks once again to all of you for your help.