Thanks everyone.

From here i decided to start under the bonnet. The engine had a misfire and water was mixing with the oil so i remove the head to investigate.







I found the water jacket next to number three piston had corroded and was spraying water onto the piston. see pics.

This is how i found the head upon removeal.



True to the last owners word the engine does seem to have beed modified looking at the ARP head bolts fitted and the porting of the head and IM.