Yes, I know about these 2 timing holes and used them. I am not quite sure how I managed to get the timing off. I suspect either the chain wasn't fully seated on the exhaust sprocket and slipped to the next links while I started to rotate the crackshaft or there was slack in the chain between the exhaust and intake sprockets and I didn't notice. I'd bet on the first one. Needless to say I'm very disapointed in myself. I'll update the thread once I find out if the valves were damaged or not.
Michael