Some good advice is take it to someone who knows these engines, Get them to do some more tests for you, don't go back to your mate unless its to pick up his share of the repair bill. remember theres not just replacing the head gasket, the head needs checking, its not a cheap job if done right, but theres no shortcuts, buy a good gasket set , and if the head needs skimming and your keeping the motor get the valves re seated and de-coked etc. like i say get someone who know there stuff, no disrespect to your local mechanic but it may be worth asking him if he as a knowledge of Landys,
Good luck...