Your better off getting a set of aftermarket brakes fitted instead of the HGT ones.
You will get a lot of benefit in just doing the fluid and a set of fast road pads, thats all I've done on my HGT and it made a huge difference. Mintex 1144's are probably what you'll need.
I'm actually interested in this idea too. Knowing the Fiat way of making things, one has to propably change the rear axle to fit disc brakes to back. This is the way it was in Fiat Uno. But is it do'able? (how do you spell this Many things in between 127/Uno/Ritmo/Regata/Bravo tech are very similar.
BTW, is there allways ABS on the HGT? Because if my 1.6 does not have ABS then it would be practically be impossible to upgrade the brakes...
I was about to do this kind of a swap (Turbo brakes) to my (very old)Uno but then I came to senses and bought a newer Bravo
there a piece of **** to change over take them to your local garage and just ack them to swap them over,its only realy like fitting a whole new set of breaks,have a word with rob d because he himself is having a big disc conversion done almost as we speak.