Thanks for doing more photographs, you neglected to do one of the right side of the buttstock, there should be an "eagle" over a letter, either eagle/H or eagle/M, though it could be obscured or worn away. Try to examine the area closely and see if you can see the remnants of a small "H" or small "M" (typically the eagle will be very small, but the letter generally larger), this branch of service acceptance will be above two Eagle/WaA623 acceptance stamps (generally they are easily noticeable, in this case, because they have escaped your detailed attention, they are probably very worn). Perhaps someone with the new volumes IIa or IIb can post a photograph of the relevant page that illustrate what I am speaking about.
The barrel was made at Steyr, Austria, from a raw forging from Poland (RD= Radom, a raw forging or barrel blank left over when the factory was captured and subsequently sent to Steyr for finishing. So Polish steel, finished in Austria, very common in 1941 production)
Altogether the rifle looks pretty original, other than the deactivation, the stock looks to have SDP shallow cutout and the internal serialing compares well with other bnz/41 in this range, - the only interesting thing I noticed was the "circled V/1" on the bottom receiver flat, I will have to review my database and see if i can find other examples. This closely resembles the "circled V/7" found on 1943-1945 Gusen made receivers, though I do not think there is necessarily a connection. Perhaps SDP use of a "circled V/#" carried over to the operation at Gusen and i never noticed it before, or it could be unrelated altogether... If I find something on this i will add my observations to this thread.