Thank you everyone for the info and comments.

Der Ami,,I won't be replaceing the stock (thank you Whitey for the offer though).
It's too nice of a piece of wood underneith the grime. I do believe it is cut down though.
Close inspection of the bbl ahead of the forend tip and of the muzzle shows the old wood line and a muzzle cap image from wear/use.
I'd thought about a splice to bring it back to length. Done back a bit further at the swivel point would help in disguising it.

But splices on long thin pieces usually end up showing themselves no matter how well done initially.
The purpose made diagonal splice with spacer isn't something I like either though I've seen it on a number of older mannlicher stocked rifles.
I'll probably re-do the forend to a standard 1/2 stock style and either use the existing lug as a front swivel base (something I've done before on a sawed 1908 M/S carbine).
Or place a separate base further out on bbl and elliminate the original swivel lug.

Sharps4590..The bbl I believe is original. It;s serial # matches not only in number but the stamp style is the same as on the action and other parts. The front edge of the receiver ring is filed to shape for the raised rib.
I'm sure Steyr would supply most anything the customer would want or pay for like any other company of the time.
Usually raised rib bbls on European sporting rifles are most commonly seen as 1/2oct or full oct styles. This one is full round tapered with a small section at the breech a slightly larger diameter. Something different, but very European. Top rib is matted. No ramp at the front sight.
The front sight insert keys into the rib directly from the front.


Kiwi..Still haven't done a chamber cast,,maybe today. Almost hot enough to melt the cerrosafe on the sidewalk.

Mike Harrell..Beautiful M/S. They don't get much nicer looking than that. I like those sights.

Raimey..Do the proof marks tell you that it was proofed at ZM? Thus the comment about 'sourced from a mechanic in the ZM area'?
I don't know how that all worked,,
From there,,on to Barella in Berlin to be retailed or perhaps sold to a waiting customer?

Proofs and the whole 'Maker to the King' thing are just a blur to me. Too confusing when I try to sort it out. The mechanics I can deal with.