There were quite a few small outfits building special stuff like this in the UK in the days before “production” based racing took over. F1 to Superbike is a good example, the last year of F1 1987 saw a Bimota win World F1 and in the same year Spondon, Harris and P&M raced in the same class but by 88 they’d all gone and production based Jap bikes took over. I believe this change happened a few years earlier in the US and Canada, the rest as they say is history.
Hagon also built a few monocoque motocross bikes. One still exists and is with a friend of mine.