I had an old mechanic tell me once that Marvel mystery oil is a good thing. You may want to try putting approx 1 oz per cylynder and let it sit a few days with the plugs in but not torqued. Then remove the plugs, let the engine crank for about 4 seconds expelling the oil. Replace the old plugs and tighten. Purge the old gas. Put fresh gas in and one or two seconds it should fire, smokes a little bit at first due to residual oil in the cylinder. Once running awhile and no more smoke, I would remove the plugs and install new ones. A basic tune up would be good with wires distributor etc.