Hi Danny /Abe,
I like these late 3rd Series or unofficial 4th Series of Mark 3s as they still retain touches that were later 'cheapened' by the factory. These include a proper contoured tap, that nicely profiled trigger, early stock medallion and lack of scope rail, which was never of much use anyway.
Based on pics, which suggest some surface wear to stock and action, a very rough suggestion from me would be £125 to sell. Clearly a shop would ask more but for a private sale on a forum like this, around £125 is probably realistic in my view.
Hope that helps.
John