Ive got the same problem atm, if you stick your foot down you see a load of smoke between gears then if your parked up and nail it to the red line it smokes bad too.
Im pritty sure its valve stems and oil seals.
If it was rings it would smoke all the time i would of thought.
Not an easy fix really. Im in the process of changing the head with good guides and new seals and also new rings and block honed just for good measure but its up to you how far you want to go with it.
If your not burning much oil i wouldn't worry too much for the time being.