Peter A Goldsbury
Do you know where the clip was taken, or who the uke is?
The location is clearly a sports hall and not a dojo, so I wonder whether the occasion was one of Yamaguchi Sensei's trips abroad. To me, the uke looks somewhat like Minoru Kanetsuka (of course in 1976 this would have been well before the onset of his cancer). This is speculation, but if it was Kanetsuka Sensei, I know from experience (having often taken ukemi from both) that he would have given Yamaguchi Sensei a run for his money.
The information on the Youtube clip reads:
Yamaguchi Sensei Summer School UK 1976.
Some resistance from uke at 1:00...
Since it takes place in the UK, the uke is very likely Kanetsuka Sensei, as you postulated. I wish there was more information about this clip as well as sound!