My first bike was a '78 Yamaha DT175. Fun but slow 70 MPH was top end.
I had a '78 DT400. I was stolen the night before mothers day of '82. Made a great dirt/trail bike - not to good of a street bike. It almost felt illegal when I road it. It was just a motocross bike with lights (and a knobby on the back). It would pick the front end up in any gear. You're right, they were fun.
I remember someone in HS (80s - so the bike was 70s) had an RD350 set up as a cafe racer. Looked pretty cool. I think it was purple metallic from the factory?