Hiya ... The 1.3 Master Cyl is slightly smaller diameter on the bore. That will increase the travel requirement slightly for that caliper. Servo will be fine. If you are ABSOLUTELY sure you bled all the air out the system, and the rear shoes are working correctly, plus any new pads are fitted/contacting ok, it could be damage to the master cyl seals caused by the travel into a different area in the cylinder (like when the pedal goes to the floor) This happens on older M Cyls. Change it if you have to.
Have a rebleed first, tho. Bed the brakes in lightly nearby first!