Yes, you'll need to cut out the crossbar.
You'll need to swap around the main powerwires; usually the supplied (JVC) harness has bullet terminals along the yellow/red wires to make this easy.
And you'll need a steering wheel control interface and patch lead. For example, the Connects2 CTSAR001 or 003, plus the CTJVC2LEAD or CTJVC3LEAD, depending on what type of plug the headunit has for the steering controls.
More details in this thread: http://www.alfaowner.com/Forum/ice-a...56-and-gt.html (HOW TO INSTALL AFTERMARKET HEADUNIT - a guide for 147, 156, and GT)
And look up the Connects2 website (or nexxia.co.uk) to check the patch lead.
!Reported: to move to ICE forum.