as far as I know it is Bob Dunn. He build me 2 engines with 636 cc and if I remember correctly he is now making them with about 680 cc as well. The engine really goes like stink. changing from a standard Comet to the 636 is like going to a twin ( not my words but those of P.Barker who rode both bikes ). Being bored and stroked the engine pulls like a train .
You can give Bob a ring, but please notice that I am in the queue before you !!!!! if that makes any difference to Bob ??....