Gotcha. JD is Jim Dunken, an engine builder from the portland area but he closed up shop in the late 90's early 00's I think. Arguably he built some of the fastest bikes on the west coast in the early mid 90's. Mostly banshee's but he also built some wicked R's. I have a 66.5 JD cylinder I want to try out someday. Let me know how you like it.