https://www.youtube.com/watch?v=_NfBYoDDdeEInteresting little video of some low budget, out-of-the-back-of-a-van, classic bike sprint racing.
The featured bikes are a pair of Vincents, a 500 single (Comet) and a 1,000 twin (Shadow or Rapide). Both are in modified Norton Featherbed frames, the 1000 twin looks to have Norton Roadholder front forks, not sure what the 500 has, and I think I heard mention in the video that the swing arm was a modified Yamaha type. No surprise both are using the tried and tested reliable Norton (AMC) gearbox.
The venue is the disused WWII heavy bomber aerodrome at East Kirkby, Lincolnshire, England.