I believe that the engines and gearbox/transaxles are assembled in England.
I am not sure if the actual block/head castings are made there or not, nor of the country of origin for all of the various internal parts.
BTW; two of the residents on my floor in the dorm way back when I attended the UofA (Tucson) were from Prescott (one had an original blue '69 Boss 302 with real Minilites on it at the time!).