A bit of a mystery then with the repairs on the stock, the rear sight is a C Mk.3 with the A inside C mark so that was replaced at one time as well. All other parts are LB marked.
I guess the wood and sight could have been swapped around anytime in the last 74 years.
Either way its a nice rifle, only issue with it is the little adjusting lever on the sight is broken on the bottom - seems pretty common to break.