Hairy potter

2 weeks ago fell for a rough old xjs v12 convertable, thats sadly been siting outside for 5 years with a ripped roof' & no key's.. now i've got it home it has a few problems to say the least' floors gone on off side which didn't put me off' I changed the old fuel in the tank tried to start it last week & found no power to the pump. I've got that running from the battery & getting fuel up to the pipes before the injectors. I used a can of easy start but still no joy in starting the old girl. dose a f reg xjs' have a built in immobobliser? as when i turn the back of the ignition barrel the horn goes off" I then tried to take a plug out & it broke leaving the tread part of the plug in the head' all the other plugs are very tight so left them there.. I understand now i might have to get it running before i can losen the plugs, when the engine is warm because of the steel to ally combination. I have a couple of questions dose this car chip in the key that i haven't got? can i change the v12 engine for a rover 3.5 v8? I have heard that removing the head on a v12 to do the stuck plug thread is a long mission because you have to hang them to losen the head from the block. But' if i can get it started i might not need too.. any advise welcome Thanks Tony