The coil-on-plug COPS of the Alfa 24 valve could work on the 12 valve engine, but you have to devise a way to retain them on the valve cover. There is another member here who has converted a clip-on type COP from another manufacturer on to a 12 valve engine with good success! (I think it was a BMW-COP if I recall correctly...)
Keep in mind that simply installing COPs won't work - you have to switch to a programmable, stand-alone engine management system - the standard Alfa/Bosch L-Jet ignition system won't drive COPs as is, right out of the box.
Just a question, why do you want to do it? Performance? The gains would be imperceptible without further mods to the mechanical plant and even then, you gain smoothness and some efficiency, but not necessarily raw power. If anything, you increase complexity and maintenance - I have personally had one fail in as little as 18K miles and most start to fail in 60-80K miles!