I'll slide out on to the ice for you Vikram.
You can call Purdey's. You have the serial number.
If you take it apart, there are enough places that a "true" Purdey is marked that you could find your answer.

To quote Crossed Chisle's, "It's like King Alfred's axe, it's had 3 heads, and 2 handles replaced, but it's still King Alfred's axe." Apologies to Mr. Trevallion.

You can do anything you want to a shotgun if you have time, money, and absent those two, talent.

Out there doing it best I can.