It's genuine and definitely not pieced together any more than other Fenders of that period. All Fender guitars were made up from parts made at different times. The vintage year is traditionally determined by the youngest dated component such as the neck, body or pots. Fender would buy bulk pots and serial number plates and they would be picked from stock bins relatively randomly so there is a fair degree of date tolerance when it comes to serial numbers. IMO a genuine period case would've added at least £500, maybe a fair bit more, to the price. I don't think the strap buttons are significant as a reliced modern pair would be indistinguishable from the originals.