The engine was originally designed for straight 30 weight oil in weather above freezing, and 20 weight or thinner in winter. You'll get lots of opinions about which gee-whiz special oil it needs now, and opinions are like - - - -uh- - - - -"noses". Everybody's got one, and some of them smell really bad!
I prefer 15W-40 diesel-rated oil because it has some additives that automotive-type oils don't have anymore. I use it in all my vehicles, from a Massey-Ferguson tractor to several lawn mowers, and all my cars and trucks. Buying it in 5-gallon pails at a good price from the local farmers' co-op is one reason, plus it makes oil changing very simple. I don't like a multi-weight oil with a 10 weight or thinner minimum rating in a stovebolt engine, but that's just my opinion.
Your white smoke could be condensed water in an exhaust system that's been sitting unused for years, or brake fluid pulled through the intake manifold from a bad brake booster, or moisture from the cooling system getting into the combustion chambers from a blown head gasket or a cracked cylinder head. If the oil in the crankcase isn't a milky color, run the engine for a few minutes to see if the exhaust smoke clears up. As long as it doesn't overheat or make any nasty noises, a little smoke won't hurt anything but the mosquitoes!
Jerry
