One of this winters mods is to remove the servo and master cylinder as I Don't get any feel to the braking, the master cylinder on there will be a too larger bore so my question is what to replace it with. The pedal can accept a bias bar so a dual system is a possible option.

So what bore size is recommended?

What have you got now? I just removed the servo from the Sierra system and drove on! 22mm bore with M16 front and Capri drums at the rear.

Not sure what is on there as I haven't taken it all off yet. Would of thought the master cylinder from a servo assisted car would be the wrong bore size and so the ratio will be out. If not then happy days !

You have to remember that my car weight way less than half of the donor Sierra

A lot depends on the pedal leverage ratio on a lot of modern cars the ratio is near 10:1 and they have a powerful servo.

Before servos became universal it was more or less standard practice to use a 0.75" (19mm) bore master cylinder on cars with front disc brakes, when a servo was fitted the bore size went up to 7/8" (22mm), Allowing for the much reduced weight & lower leverage ratio which more or less cancel each other out a 0.75" bore tandem cylinder should be ideal.