Don't go near Halfords unless you're made of money! I did the wife's 147 with these:
http://www.ebay.co.uk/itm/Single-DIN-Pocket-Tray-Double-Din-Adapter-FP-016-/250598245407?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a58d1c41f
http://www.ebay.co.uk/itm/CT23AR02A...arts_Vehicles_CarParts_SM&hash=item2a157ff925
http://www.ebay.co.uk/itm/ALFA-ROME...cles_Terminals_Cabling_ET&hash=item3f0ea178bd
Obviously, the last one will depend upon the make of stereo you're using. You'll probably also need an ISO harness adapter
When you connect the power wires, you will probably also need to swap the switched and permanent live wires, if it keeps blowing fuses - Alfa didn't wire their cars up like everyone else.
http://www.ebay.co.uk/itm/Single-DIN-Pocket-Tray-Double-Din-Adapter-FP-016-/250598245407?pt=UK_CarsParts_Vehicles_CarParts_SM&hash=item3a58d1c41f
http://www.ebay.co.uk/itm/CT23AR02A...arts_Vehicles_CarParts_SM&hash=item2a157ff925
http://www.ebay.co.uk/itm/ALFA-ROME...cles_Terminals_Cabling_ET&hash=item3f0ea178bd
Obviously, the last one will depend upon the make of stereo you're using. You'll probably also need an ISO harness adapter
When you connect the power wires, you will probably also need to swap the switched and permanent live wires, if it keeps blowing fuses - Alfa didn't wire their cars up like everyone else.