Yeah tried to find the same 600 stuff on t'interweb, found one rear mech that looked the same 1978 version IIRC, will try to find the date code if it has one.
Give the tubes a flick for rust befroe you set out on the road on it - there might be a very good (but not obvious from the outside) reason why it was skipped.
It's pretty solid, minimal rust, quite a few battle scars on the paintwork, but not much of the dreaded 'R' word
The cassette is a bit worn out, the (new) chain jumps a lot in the smallest sprocket, so I have temporarily adjusted the H limit screw so it doesn't get that gear.
It did look really tatty until I got a rag out & gave it a quick once over, will do a thorough clean later when I have time.