This is a good thread too:
upgrade master brake cylinder
To my knowledge, there are no exact rebuilt replacements available and there is no kit available (The one from Dorman is for drum/drum).
The later '73 on up style iron 15/16" bore ones will work fine however they are larger in size. The 15/16" DoctorDiff, while looking more modern, is a welcome 'no leak' style.
I recently did the DoctorDiff. Until my stock one started to go bad, it was a very hard pedal. The DoctorDiff is definitely an improvement.
View attachment 1715655422