Motorcraft plugs worked well in the 1.3 and 1.6 crossflow engines, and the fat ones in the pinto engines, but the 3.0 V6 preferred Champion plugs. The Cologne V6, 2.3 & 2.8 always ran better on Bosch plugs, and ran poorly on Motorcraft.
No idea who manufactured Motorcraft plugs, I don't think it was Champion. They may well have had their own manufacturing plant for them. Ford did used to make a lot of their stuff themselves.
Ah yes, The "fat" pinto plugs. Were they exclusive to the Pinto engine? I never worked on anything else that used them.
Quite a few years ago I came across a very old cylinder mower - It's a Ransomes Minor Mk6, I think it was made in the 1940s or maybe 50s.
My father had a very similar Atco machine in the mid 50s which I remember very vividly due to the fact that he always had extreme difficulty getting it started. My Dad's machine had a foot operated kick starter whereas mine has a starting handle. I think a lot of Dad's problems were because the kick starter only allowed you to bump the engine over one, possibly two, compression strokes so you couldn't get it really spinning, Ransomes way of doing it with a proper handle is likely to be much better. Both machines had a Villiers midget 2 stroke engine and the one sitting in my shed, which may be this winter's project, could do with a new spark plug. Guess what's in it at this minute? - One of those "fat" pinto plugs! It's obviously not the correct plug as you can see the seat in the head is machined to accept a sealing washer but the threads seem to work and I don't think they are damaged.
I need to explore where I can get the correct plug but, as the coil seems to be jiggered I'm going to attempt to source one of those first.
Interestingly there seem to be generic coils, in a big range of dimensions, available from the east and I believe old stock genuine coils are dodgy due to the lacquering on the wire being prone to breaking down. Think I'm going to try one of these, probably Chinese manufactured, lookalikes.