I think if you are using the Sierra master cylinder you need to check the holes line up with the break pedal.
I seem to remember the large center hole was in the wrong position.
I can't remember which way it was out, but I do remember I had to modify it after I was finished.
Also it may be worth thinking about a clutch cable adjuster whilst your at it.
Crabby pic I'm afraid.
It's the yellow bit
I made it from a piece of 19mm threaded tube and a couple of nuts for adjustment.
David