They are old and brittle and curling up on the ends. Need to soak some.more with silicone and then try to glue the ends back down. They seem tight though other than that. Wierd how this frame sticks out so far on the outside.
https://www.lehighvalleyabrasives.com/non-woven-abrasives-clean-and-strip-it-discs
https://www.lehighvalleyabrasives.com/non-woven-abrasives/surface-conditioning-discs-4-1-2-x-5-8-11-non-woven-fiberglass-backed-t27-clean-strip-disc-black-coarse-cs4-5-crst
With these you can do the whole bed...
Agree with Snoots. Had the same issue with a 79 Vette we had once. Pulled the distributor and replaced the ickup coil. Problem went away. Probably easier to just replace the damn distributor though unless there is something special about that one.