This one reminds me of the first lightweight track bike I raced, around 1965 after giving up with my Aerial 500 twin(shackle heel rear end, try that on a scramble track). It was a 197 James, with a motor which had seen service in a go cart, so was quite heavily ported. The megaphone exhaust made it incredibly load, but it could hang with the bigger bikes on a scrambles track, easier to ride. My first vision of the future!! It would make a very competitive pre60 bike today - might have to fit some sort of muffler though.
Mike