dont use a cheap gasket I had 3 cheap ones blow finaly got a heavy duty on its got 2 metal plates each side not had a problem since, because I have done a few it takes me five hours from start to finish the bigest job is cleaning the old gasket off without damageing the block or head I use a gasket scraper to get the heavy stuff off being very carfull an old way of cleaning the the last bit of grim off the head is to tape a peice of fine say 1200 grit wet and dry to a peice of flat glass put some light oil on it and lightly rub a figure of 8 with the head on it, its very important not score or damage the heads surface or block in anyway, the one thing I found caught me out doing my first disco 300tdi head as apposed to a 90 300tdi is that on the disco you have to put the end 2 head bolts in before putting the head on as you cant get them in under the bulkhead I use some insulation tape round them to stop them dropping down to far so thy dont contact the block on refit. like is say the clean up of the surfaces takes hours and for me the biggest pane of the job if the heads scored or dameged in anyway it wil need a skim or even replaced