Hook, as Rothhammer mentioned it you probably own a 'transitional' piece that went out the factory after the Anschluss but was made using existing pre-Anchluss factory stocks.

The rationale for my assessment is the following:
- Action still bearing the 'Made in Austria' that came into force after WW1 (but it took some years after 1918 to have all new rifles bearing this marking, probably due also to existing pre-WW1 factory stocks) until in theory the Anschluss in March 1938, from when all new rifles should have been marked 'Made in Germany' (again it took some time to have this enforced for multiple reasons).
- Mention of calibre 6,5x54 NORM ('NORM' stands I think for 'Normale Patrone'), which was the post-Anschluss marking for the earlier Austrian model, which was stamped M.1903 only instead of the caliber, as all M.1903 were in 6,5x54.
- In addition to the marking '39' (proofed in 1939) that your rifle bears, it also bear the marking representing a two-headed eagle with a shield on its chest; this marking was up to my knowledge only used post-Anschluss. You should also find a number in the shield on the eagle's chest, if it is '1' it is for Ferlach while '2' is for Vienna.

Of additional interest might be to see what the factory marking on the left side of your rifle's action is:
- Until 1924, the marking was 'Oesterr. Waffenfabr. Get. Steyr'
- From the M. 1924 model to the Anschluss, it was 'Steyr Werke A.G.'
- And from the Anschluss in March 1938 until production ceased at the end of WW2, it was 'Waffenfabrik Steyr'.
Again this is the theory but in practice, due to existing factory stocks and other production reasons, transition took some time to happen in some cases.

For information I own a M. 1924 in 7x64; this rifle bears:
- The Austrian Vienna proof marking NPv as well as the xxxx.28 (1928) factory number, so definitely pre-Anschluss.
- However it is also marked 'Made in Germany', '39', and 'Waffenfabrik Steyr' , all post-Anschluss markings.
So I assume this rifle was produced at Steyr in 1928 but was not proofed until 1939, hence the existence of both pre and post-Anschluss markings.

Anyway welcome to the Mannlicher Schoenauer maize!

Louis