68 Z/28 Engine Smoking - Any Ideas?

[68 RS Z/28]

Thanks for the suggestions guys. The engine was done around 5 years ago so I doubt the engine builder will remember exactly what he did. I do know it was new valves. I'll check to see if valve stem seals were installed, but I expect so. I've been dreading rings as the problem....definately not what I wanted to hear to be sure. If it broke a ring, wouldn't there be other issues (noise, debris in the oil pan, etc)? If the rings aren't seated, is there any way to do this now without ripping the engine apart? I'm not a complete novice, but I confess I have no idea what the difference is between low tension oil rings and standard oil rings. Thanks again for the suggestions.