Got it tested darren, came out fine.
It wasnt warped either, so must have been the gasket.
It was corroded near the water channels so perhaps it was enough to build pressure in the coolant.
Im glad i did it anyway, the head and valves were badly coked up so ive cleaned both and il grind the valves in so it should be a freer flowing head when i rebuild it.
Ive new stem seals as well to go on.
It will eliminate the head if it doesnt work.
Could possibly be a cracked block? How likley is that?