Mario,
changing the head gasket on an XK engine is neither rocket science nor does it require special knowledge on rare automobiles. What you really need though is plenty of room for some time and heavy-duty equipment. XK heads are notorious for entering a very tight relationship with the blocks. A mechanic once told me he had lifted the entire car up on the rings of the cylinder head and only after days of load and the action of penetrating oil the head finally gave. Use of bottle jacks also seems to be a proven tool to get the head off the block.
Given all that you might whish to seek for a mechanic who simply works carefully (doesnât bend the valves once the head is down!) and thinks twice before resorting to bodges, to help you out ⊠Once youâre in the rest should be easy, unless there is further damage.
Good luck
Jochen
75 XJ6L 4.2 auto (UK spec)