I'd hazard a good guess that 73 looking at the helmet design is Nick Jefferies - the RG 500 in trad BMW Motorrad / Sport Allan Jefferies dealer colours must be Nick but prepared to be wrong.

Cheating slightly just checked the results No 70 - the early model NS500 triple 2-poke but late starter number 70 could be Peter Linden ?.

Another piece of lovely memory looking at the 1984 results is the late Sam McClements on a Keen RG500 Suzuki - at the moment i'm helping Mark Keen the son of the late Roger Keen prepare/restore some of the various racing TZ / RG 2-strokes that Roger collected over many decades at his workshop in Aston Clinton.