IMO save your money and don't bother with an oil change. Use the money to let a garage check it out and diagnose the problem, which I'm affraid to say does sound like a piston ring.
But hey look on the bright side there are plenty of second hand blocks about for little money, and plenty of knowledgable mechanics about to drop it in or even repair your unit. I'm sure there is a few on this forum that could help you out.
Hope I'm wrong for your sake, but blue smoke nearly all the time = Bad news
