Alf was a demon on the bike, but riding down the middle of a busy dual carriageway is going to skew results. It is why people went to those courses and I know you still have to pedal and breathe, but assistance is assistance.
I remember testers scoffing at times set by particular riders, on the drag strips, and from my one go at a 30 ,on one of them , i understand how that came about. I could never have done 27mph average, over 30 miles, anywhere else. I wasn't even on a lo-pro ffs!
A real test would have been an hour record attempt back then and then time machine him to present day to have a go on a current track bike.