Whats the differance between the 2.4 and its Alfa cousin, is it just the mapping or any engine parts ?

How much work do you think it would be to get one working in a Brava, how are the looms on Fiats, all in one or sperate plug in parts ?

Provided you're talking about 2 valves per cylinder and the same age of engine, then they are likely to be identical with just a calibration change for a few more horses. The later Alfa's have moved onto 4 valve heads and with the latest Euro 4 emission requirements have some other differences including variable geometry turbos.