You may have just had what I failed to relate in our phone conversation. You can't help but spill some gunk into the exhaust pipes as you tear down and rebuild. That has to burn off. Two, your rings may not have fully seated at first, so some oil makes it's way past and burns up. This is worst at high manifold vac during prolonged idling.

I'd let it idle for maybe 20min or so, and then blip the throttle and see if you still get a puff of smoke.

Not responsible for advice not taken...