In my experience, an engine that's been sitting for a while may smoke for a
considerable length of time. Hundreds of miles, under load, not just
idling.
If it runs well and doesn't leak any fluids, ignore the smoke, don't go too
far from home, and start driving it regularly. Worry about it if it is
still there after, say, 1000 miles. "Just my humble opinion based on
limited experience."