Hopefully i can help..
In all probability its most likely the Headgasket..of course you can never really tell if the cylinder heads at fault without actually having it pressure tested off the engine,usually that has to be carried out during a headgasket change where overheating has occurred for a prolonged period..if the head shows signs of problems due to the overheating then another cylinder needs to be sourced.due to either a crack or warp issue with it due to overheating is normally whats happens..A normal coolant system pressure test can be done on the engine as it stands at the moment and see if that shows anything up or if possible compression test at least on all cylinders..considering you do have the smoke.vapour from exhaust pretty much confirms coolant is being sucked in and burnt during the combustion cycle..I do hope this helps..If you require to ask anything further then please continue before you rate
Thank you Robert, your help was usefull, I did have a feeling it may have been the head or gasket. I have since had the engine rebuilt so hopefully no problems will now occur
once again thanks