lo mate,
yes the willy/16V/GTT 19 16V calipers will all bolt straight on no problems. Old ones off, new ones on.....inc the discs.
They DO, give better braking, and performance braking parts are more readily available and cheaper.
Some people report no change in brake pedal travel, whilst i have noted an increase in mine, so i replaced the master cylinder with a 16V item. problem solved. Yours right now might just have a air block in them.
Overall, an easy and worth while mod.