A puff (or a cloud) of white/blue smoke when you punch it after coasting is usually valve guides, with really bad rings a possibility. If you can't live with it, you are probably looking at a complete overhaul. If you're really lucky, rings and bearings and a valve job will do it, but the bores are likely worn enough to need reboring. If its a "Beater" that you like but don't want to put a bale of fun-tickets into, find a good used engine at a wrecker's.