As an FRST owner I would always say fit a turbo cvh unit to start with anyway , if you then go zetec after then you still have the cvh to go back in to keep it original , you could always go the zetec route straight away as you say you are going to rebuild using forged pistons

On the gearbox front , you can tell an LSD box by looking through the differential , if there is a pin in there it is a std diff , if a hole then it is an LSD .