-JdK- Viktor provided this very useful info for those looking for pistons for their vintage Norton.
"Here is a description and a few images of new pistons. Pistons with a 5/8" pin and fabricated according to the original 2797 Hepolite piston dimensions are being produced by a specialized manufacturer in the Slovak Republic - go to www.ceba.sk for more information.
You will need to provide them with the exact cylinder bore. Pistons are supplied including three modern piston rings. Delivery time is around two months".