Yes 15/16" bore front cylinders from December 1953 according to ESM who also sell the repair kits for the genuine Lockheed cylinders.
Having never tried to repair a cylinder (they've always been too corroded) I can't answer that bit. The seal is in the bore, not on the piston so you need to get the old seal out without scratching or damaging the bore. Then you need to get the new seal in without distorting it. Bill posted a tool that makes the seal a heart shape to fit it. Not sure how you get the old seal out......some kind of hook tool like for rubber o-rings I think. There are videos around of how to do this.
Stephen