You need an engine, trans, new radiator, engine mounts and all the other little bits and pieces such as hoses fuel pump etc, etc.
I did the swap in my XF and it cost me $1300 for all the parts to swap it over from a six. It cost me $1200 to get it all fitted including a new set of extractors attached to my old exhaust.
Do you live in melbourne? I bought all the gear from just falcons on canterbury road, if something was missing i could go back and they would give it to me free, They are good blokes. They will do the fitting as well for around $600, I went somewhere else for the fitting and that was a bad a idea.