Spray the sparkplugs with a good quality rust lubricant like WD49, Kroil, PC Blaster every day for a week. Crack loose sparkplugs, remove them and fill each cylinder with bulkWD40, Kroil, etc. Keep topped off and allow to sit for possibly weeks, checking on each cylinder fill. Try after a few weeks and see if the engine will turn over. If it turns over then drain engine oil and refill with new oil for first attempt of starting. Clean out fuel lines, fuel tank and refill with fresh gas. You can then begin to try and start engine. Piston rings may free up after running for a while. Be sure ignition system is in good working order.