An old trick I heard of was to use kerosene. Maybe get the engine warmed up, take the rocker cover off, pour the kerosene on the rocker arms, remove the rocker arms, pour the kero. down the push rod(inside and outside), use a piece of wood to work the push rod up and down. Change the oil. Let it run , change oil again and good to go. I would think it would be worth it to repeat the process a couple of times if you didn't see improvement first time. As far as the smoke while running, sounds like maybe a stuck piston ring or three. Remove the plugs, pour kero. into cylinders, do not install plugs, crank engine(it will be a little messy-use rags at plug holes). Change oil twice. A good machine shop should be able to just point out the areas that need attention. Keep in mind that this is an odd ball case in the fact that any other engine with 80k miles would still be running, not needing a rebuild yet. There will be some areas that might need work that ordinarily wouldn't. I would get a 5gal. can of kero.(cheep), and work the dog snot outta it. Let it drain into pan and give it a couple of oil changes. This is a little more than $.02 huh? hehehe. Good Luck. BTW Marvel mystery oil is good sxxx.