at your parts house look in the rear piston "thimble" & for a manual brake app it needs to have the circular recess about halfway down for the neoprene nub on the end of the manual brake pushrod to lock into. A PB app does not need the recess but is fine with it, not so with manual brakes, must have. then as you are doing, get the right bore.
I would be interested to know if the manufacturers make all their mc compatible with manual brakes if they can also be used on power brake cars but not vice versa.
