What color is the smoke? Blue tinge? White? Black? Rings could be the problem, but also valve guides. I'd wonder what it looks like inside. The problems mentioned by Bill are possibilities. Engines that have been sitting, are 'suspect' in my book. So many things could have happened. Like a little rusting in the cylinders, which if severe enough may prevent the rings from seating for a long time. Is it possible that new rings, in new pistons, could have become stuck from sitting. I doubt it, but if so, running it awhile should free it up. Also, rings made years ago are suspect, at least in my mind. It's my belief that current rings are far surperior to ones I bought in the 50's. I suppose if it were mine, I'd already spent the bucks, and I was committed to it, I'd try running it for quite awhile, and see if it improves. If no improvement after a few K miles, I'd want to open it & look-see.