You can convert using all the bits you have bar the exhaust manifold, but you'll need 3d ignition as a minimum I think. If you have the budget I would go with TBs. If not keep your 45s bearing in mind that many people (including myself) have had issues getting the fuelling right for a zetec on progression (snap throttle) and also on idle.
Recent personal experience would suggest that there may be some benefit (if you fancy trying it) in modifying your carbs to accept fuel injection rather than going to TBs esp as otherwise going to TBs was expensive. If you do go to TBs consider you need an ECU and think about who you'll get to map it for you. If you're nearer Ipswich than London you might wish to get Emerald and use Dave Walker. If not you're off to see Steve Greenald near Rainham, London. Also take advice on which fuel regulator to get, which fuel pump and injector combo for the power you're aiming at too.
Bear in mind that the zetec won't have that frantic urge of the XF, which can be disappointing until you install some hotter cams, then things get a bit more spicy, but as standard it's undeniably faster than alightly modded XF.
You may need a new fuel pump whichever way you go and yes you will need to consider corrosion more often than before. Hope that helps;bet I remember something else once I press send.