Re: Spark plug
You could try checking the hole size, the really small ones have 10mm threads, then there's 12 and 14mm as common sizes, then you'd need to measure the reach... basically how thick the metal at the hole is, common sizes can be anywhere from 10mm to 20mm. Also with the reach determined, you'll need to buy a plug with that reach then slowly turn the crank by hand to ensure the piston can't hit the plug electrode. If you can remove the head easily, putting a small piece of modeling clay on the top of the piston is an easy way to measure clearance, or if the plug is recessed in the combustion chamber god enough, it should be a non issue.
The engine should run once you get the right thread diameter and reach, then you'll need to find out the right heat range which unless someone else knows, it's trial and error. Starting with a cold plug and working your way hotter until the plug can "self clean" is the safest method.
Pretty much all you'll need is a source of some really cheap plugs until you find what works best.