[tony58]

ALL disc brake C20's came with power, all disc brake C10's came with power until 1974 when manual became available

ALL C20 power disc brakes used a 1 1/4" master due to larger caliper piston diameter.
All C10 power disc brakes used a 1 1/8" master while the manual versions, 74 and above used 1" bore master.

If you have the large bore C20 calipers you might try a 1 1/8" bore manual master but it may be too hard which I would use a 1" bore for manual.