The only thing worth doing is replacing the whole beam with one from a GTI as they have a built in ARB, and if you do so make sure you fit nice stiff poly beam bushes & braided brake hoses all round.
If you do this you'll need to fit a front ARB to match ideally, but if you have a 1.8 Driver or GL you should already have one

As golfvr6-is-back says doing the brakes on their own isn't worth it as you wont notice much if any extra braking performance. You're better off fitting GTI discs & pads on the front
