Back in the sixties in the UK most Cafe Racers, in the sense of racing out of the cafe and back, were stock bikes or maybe slightly modified. What the rest of us built were bikes that we modified to look like the race bikes of the time. We wanted to look like we were doing a hundred miles an hour but rarely came close. My first bike had a Villiers two stroke motor and I ported that and fitted an expansion chamber and made the bike as light as possible and fitted low bars, rear sets and a bump stop seat. So there were two lots of people selling parts - dress up parts and go faster parts.
Many riders fitted fancy gas tanks and swept back pipes and a smaller group fitted hot cams and pipes and so on and an even smaller group fitted both.
Back then, bikes were really slow and did not handle very well. On top of that, most of us in the UK didn't have a lot of spare cash. I think we all aspired to own a Triton or NorVin or something powerful that handled and on which we would look like gods.
By the time the seventies and eighties came around, bike started getting faster and eventually they also started to handled better and stop effectively. Styling also changed and the classic cafe racer look for that era faded into history like bell bottom pants.
To me a small bike in the cafe racer mold is a KTM 390. Or even a modern 300 twin. If I wanted to build a sub 500 cafe racer today, it would probably be an RD350 or 400 or SR500 single. Light and easy to ride and lots of fun.