What Pa Norton did, would not be impossible today - in fact it might be easier.
I believe that many of us limit ourselves with our own mindset. Some time ago I made a frame jig to make an Aermacchi type frame for the Chinese laydown 125cc dirt bike motor. These days a few people ride CT110 Honda postie bikes, but they are very pedestrian. It would not be difficult to make something much more attractive using Chinese parts. In Australia, a Lifan 125cc dirt bike motor costs $420 - brand new, delivered to your door.
Wealth is created by adding value.
A Seeley frame with a Zongshen 961 Norton motor might not be all bad ?