Sounds like a hell of a find. Do everything you've been advised to do (clean oil tank, oil lines, remove sump plate and check gauze, oil pump - can inspect dynamo chain at the same time, oil to rockers, etc). I reckon if you're removing the rocker inspection covers you could have a look at valve clearances and you could stick some new plugs in it. Also worth checking the primary chain tension and oil level, and operate the clutch a couple of times to free stuck plates.
Fuel and carb would be my next focus, after such a long layup, there may be gunk in the carb and the tank, including the taps. Should be pretty much there after that.