Its a lovely example,i think its 1979 as number 20400 is also of 1979 vintage.

Butt pad is right for the year it may be a bit soft on the edges by now like mine.The stock is the better early MK1 type with its deep hand cut checkering it should also have a palm swell which you can see & feel on the pistol grip.As Muskett says the colour should show the grain the later ones are very bland.

The fore sight is interesting as it is the fixed post type which the sport "Sport" had as opposed to the Target "Sport" which had interchangeable elements.