"When on a autoland on the 757 cat 3b with 3 autopilots engaged you have no manual rudder control. after landing you need to disengage the autopilot to be able to taxi off the runway"
Are you sure about this? Boeing rudder systems are designed so that you can take control of rudder operation during rollout mode by manually overriding the cam/roller mechanism of the Feel/Centering& Trim Mechanism. You may have to push harder than normal, however. I'm not sure if the A/P would remain engaged if you did this.
Rgds.
NSEU