I don't have pictures at the moment, but can take some tonight.
Like I said, there is a smaller plug hole that fits a 12mm NGK plug (type D) and there is a larger plug hole at 14mm (NGK type B). So that must be the case, somebody must of bored out a larger hole and tapped it. So you just find a plug, with the larger thread diameter, that would equal the performance of the stock plug -- a NGK D-8ES-L??