When I lived in Tamworth Staffs the guy next door worked in the competition shop (they all say that) until I watch a BSA DVD with him working on Jeff Smith Gold Star Scrambler, as I understand it from him that the engines from 5985 onwards on the production line went to Super Rocket or RGS as required, its a pity my Super Rocket is 50 numbers out.
That would have been Fred Barlow who was also a great source of information on Norton Commandos. Sadly he dies a few years ago of liver cancer.
I popped into his shop once and Jeff Smith was visiting from Canada (I think) and we had a cup of tea together.
Great bloke and sadly missed.