All the 330 cars use exactly the same caliper setup. You can use the 3 calipers from a 3.2 litre version of the GTV, GT, 147 or 156. Full kits including new calipers, bolts, lines, discs and pads run to £900 all in. It is the best way to go. Alfisti.net do a good package and with exchange rates as they are, they work out well priced.
All the main Alfa specialist garages do a kit for this inc Autolusso and Alfa workshop. (Other specialists are available)
The swap is a half day DIY Job if you take the time to clean up the wheel arch, brackets etc.
I'd suggest Brembo discs as they come with zinc oasis are coating to resist rust or MTec for the same reason. Pads can get pricy but don't need to. Feredo, Brembo and EBC all do grippy compound pads for about £100-£125 Performance friction pads, while highly rated, top £200 which is taking the MIck.