Hy Red63, There are two different dual master cylinders (clutch and brake)listed for your 63 C60 one with a 1 1/4" master cylinder bore and the other with a 1 1/8" master cylinder bore.
The following are Raybestos p/ns and both are available at RockAuto
1 1/4" bore p/n MC19089 $131.79
1 1/8" bore p/n MC34404 $46.79
Hope that helps.