it's fairly easy, but when i was doing it regulalry all them 18 years ago, i was working on the belt driven 12 valvers and they had a tendancy to bend the hends if you undone them wrong or if they were warm even, total cooldown was required, overnight type of thing

plus they had 4 different thickness head gaskets depending on how much you skimmed them

alex f is the guy you need to speak to though as he teaches bmw fixers how to fix bmws