I've just done a HG change which so far seems to be a succes, if anyone is attempting to do this job DIY, I would recommend that you take your time. Source as any parts as possible before taking the engine apart and it will make life much easier. Ebay is a great way of saving money but the conveniance of a local motor factors such as Partco is worth paying the extra. Take your time, place the bolts in such a way that you are able to remember where they came from, I kept the bolts in the actual bolt holes where possible and layed the parts out rather than making a random pile. Cleaning is also very very important, buy plenty of 3M Scotch-Brite pads, they're in Asda, WD40 is good for cleaning too.
It isn't a job that you need to fear, I managed it, just take your time, do things in a logical order and don't just dive in. There's plenty of great info on the forum, other members will give great advice (don't be afraid to ask if you unsure) and a decent workshop manual is essential. I wouldn't be afraid to change another HG, I wouldn't look forward to it or enjoy it but I'm sure that if it does ever fail again I'll change it myself.
I made a thread on the forum which was primarily done so that I can show others what progress I'm making and it was also an ideal place for me to ask any questions about the HG change as I proceeded. My thread is here
. It may be of use to others in the future, it's not a "how to" guide but it does have quite a lot of info and also a bit of chit chat/banter too.
For anyone facing this job and about to tackle it on their own, you have my full support and also that of the other forum members.