I had a (I think) '77 vintage CanAm 175 qualifier (the rusty red one with the lay down shocks in the back) with a street plate on it back in the early 80s. That thing was a blast (until it ate 4th gear). Great power, quiet, easy to ride, oil injection, cushy legs. Yet ANOTHER bike I should have kept.... *sigh*
The guy on the YZ in that video restores bikes for fun and it very good at it. But he seems to have no interest in riding vintage on dirt himeslf. He just sold a Bultaco 360 Alpina. On the street he rides a daytona 400. The other guy rides a '76 honda 750 hondamatic (!) on the street for fun. But again, no go for vintage on dirt.
You have to convince your buddies to get vintage bikes and then you can all go on a retro trail ride.The very first Can Am 250 TnT's were sure ahead of their time and they are road legal.