The brake set seems to Shimano 600, not sure about the crank, possabley a suntour unit, front a rear mech a shimano but pre indexed gears. The shifters are a clamp on design with cheap plastic levers.
I dated the frame aswel as either an 76 or 86, the components are certainly pre 86, so i would reckon some has been messing around with it at so point.
The frame is very very similar to the reynolds 501 RX100 of my father in laws but that has only one sset of bottle bosse's as this has two, but no sure about the forks though, theres no provision for mudguards which would surgest a racier model.
The gent said the bike has been in a garage for years and doesn't know much about it, i noticed the rear cable layout and presumed it be a 501 frame.
Thanks for the reply.