I dont know much about tractors but sparkplugs are a slightly different case as I am trying to find as many sparkplugs as possible in the 14mm by 7/16 reach and similar to the H10s which were used by Lincoln and Ford from about 1938 up until the 1950s.
It is not a good idea to use two gaskets under the sparkplug as this changes the actual location of the spark itself in the combustion chamber. H series Champion sparkplugs are made in (cold) H-9, H-10,-H-11, and H-12 (Hot) heat ranges. Following is a list of sparkplugs that are very similar to the H series sparkplugs.
The reach of the sparkplug is the Nominal distance from the shoulder of the sparkplug to the end of the sparkplug threads themselves. It is not necessarily the full distance of the end of the plug as there is a condition called a skirted shell that extends the spark out further into the combustion chamber and also there is another condition called Extended Core Nose that does the same thing but without the Skirt. One of the things not mentioned is the starting of the engine at night darker than pitch if possible and look at the wires and so forth for blue tracking electric signs meaning you need to replace the wire, even new wires can be faulty or any other parts of the electrical system.
All Sparkplugs are 14mm by 7/16 Reach by 13/16 hexagon.
.4316 & 216
RH10..........4616 & 216
RH10C.........4616 & 216 OLD H12
H12...........4316 & 216 .................43LS.......437
R means resistors on Champion, C means a Copper core wire, and none of the Champion numbers have Extended Core Nose Plugs("Y"). M.L. Anderson