The lads at Bewley Motors finally got my engine out and sent it off to the M.G. XPAG engine specialists. This is what they found. With the wrong head gasket fitted, it is no wonder the AA man diagnosed a blown head gasket, but the real problem was the blocked water-ways in my cylinder block - that was why I was over heating. However, by the time they had my engine in enough bits to see this problem, they had found all the other problems.
Murray, understandably, is very depressed about the whole affair.