Matt is correct on the 'B' prefix identifier.
As I understand it, the 'B' denotes a rifle rebarreled by Gibbs. This one, of course also restocked by Gibbs.
I've had a couple like this - one a takedown.
They are really great and under appreciated rifles - yours, with a good bore should be a joy to use!

Cases can be made from 303 British and the dies are the same as 6.5X54 Mannlicher. I have a set I'd sell you as well as some bullets if you have trouble sourcing them.

My brother was quite successful using denatured alcohol to strip an antique chair which had a dark, heavy coating similar to this.
May give that a try,