FWIW, one of the riders, Vic Eastwood, was at the '76 USGP, which was the first MX race I ever attended. Eastwood was the guy that Rex Staten brawled with.
By '76, Eastwood was riding the only 4 stroke in the field, a CCM.
Having learned to ride on early 70's bikes, watching this video was a blast from the past. Watching Bicker's weight the outside peg in the turns was showing how much skill it took to ride those under suspended bikes. Great video.