Hi Joseph,
The easy way to add a servo is with a remote unit that can be mounted anywhere! TT3949Z is the part number or the servo on it's own is a GSM125! the later cars had a servo and master all in one but are very exspensive to buy new (if you can even find one) S/H is always an option. Just remember a servo will only assist the braking and doesn't actually make your brakes any better it just means less effort is required in pressing the pedal.
Be Safe
Oz Cooper
Classic Mini Guru UK