I recall those Bridgestone bikes... they were quick !
Which I would have agreed with, as the one on screen with the girls...
Until I saw this Yamaha, posted below. It's a 63 YG-1 80cc.
The chrome air cleaner disk to the rear of the cylinder head area matches the bike onstage.
There's a 3k x 2k pic of it online... too big for BBS'es!.
That was about the time Asian bikes impact was noticed by domestic and British manufacturers.
redk