This type of intensifier is made of fiber board and mounts on the coil box servicing all four plug gaps at once. A number of different companies offered similar units.
My old dad used pearl buttons to do the same job.
So this is just making the spark jump to the other brass nut on the board?
Kind of scary if you develop a gas leak.
This idea actually works pretty well. Years ago, we had an old 9N Ford tractor that fouled plugs regularly. We used to cut a 3/4" or so piece of fuel line hose and push it down on the plug, and pushed the plug connector in the hole in the top. The air gap was all it took.
Not much good coming out of Newark NJ these days!