Update
A few pics to bring you up to date with progress.
The exhaust down and upsweep pipe he made over the weekend and now needs final TIG welding, the end can is a hybrid of a B50 and modern Bonneville exhausts.
The air filter is from a VW camper van, the alloy side panels he made from material salvaged from a quad bike that was being scrapped on the farm. All brackets and supports for the cycle parts he makes himself from materials he has at hand.