Headgasket will cause smoke if your burning oil or water or both. Check oil colour, if its milky then gasket has gone between oil and water jacket. Take cap off cooling system resevior then start engine and rev a little, are there bubbles or water squirting upwards, that'll be gasket blown between water jacket and cylinder.
I'm not to upto date on the engine itself but possibly the cam belt has jumped a tooth which is something I would look at if gasket checks out ok. Not sure if this engine will foul the valves on one tooth out, some will, some won't. But it would explain smoke on running if gasket is ok.
Personally i'd do gasket checks, then check its timed up ok. Then i'd start scratching my head.....
good luck fella.