What a cool rifle!

Purdey action, loaded chamber indicators, stalking safeties, nice little flip sight setup...
Looks like the left barrel has straight rifling, the right with slow twist.

And three and a half drams?
Whoo-golly, that thing's going to sing.
Load up some roundball and shoot the thing!
Actually, I'd have the wood off it first and take a peek at the head of the stock, look closely for gaps or cracks.
The barrels look to be in good shape, have you closely inspected the barrel-to-rib connection?
I doubt those ribs are loose, but it deserves a look.
Is the action tight and on face?

--Tinker