Corner speeds were high because...drum brakes! I rode behind a friend on a Maico 490 once, and he absolutely flew into the first corner. He was used to riding a bike with modern brakes and couldn't slow down. Instant lesson on corner speed.
Of course the tires back then......not so great. The helmets look safe though, and are fantastic for eating a bowl of pad thai from after the race
So much to love about that video! The fact that a 500 with less power than my KK's KTM was a "big" bike (yeah, no tires or brakes I get it) ... that their airfence was a four-story apartment building ... that they have to push-start their bikes while banging into each other like drunken freshmen ... it's all so charming, terrifying, and genuinely funny at the same time.