Try your vintage Volvo supplier. I understand they came on the same period brakes for the Volvo's. Not sure if it was the S series or the P1800's. they will know. Just be sure to give them the diameter of the puck. When you get the kit, put lots of silicone grease under the dust cover to help retard moisture as this is what kills the pistons. The pistons rust up and freeze in the bore. This was also the reason why the early 105 production cars that had Dunlops installed on the assembly line, went over to ATE in the mid 1967 year production was due to frozen brakes.
The Volvo P1800 is the most common car with the same Girling 12.5 lb.
caliper as the Spiders. As Van said, Don Thibault at
P1800.com | 508-888-9715 has
stainless pistons available and may have some rebuilt caliper units
too.
This information came from the 750-101 discussion group.