I have used a clutch master from a 80's bmw 5seires if i remember right. They are shaped like a pencil and not much fatter about 12-15mm in diameter but a bit longer than most masters.

It is a pretty big job, take the dash facia out and you can see the room you have, it will run just left of the speedo cable. Im putting the brake master there also so room is pretty minimal. You dont need to take the brace out.

Have a search once the pictures come back, plenty of people have put them there.