In general the early full stocks had an 18" (actually 17.7")barrel.
In 1929 that should have been a 20" barrel on the full stock Austrians.
(In the 1950's the 6.5's predominately had 18.25 " barrels on the full stocks.)
It would Be a rarity that the receiver ring would be reworked to copy the factory, but not impossible for a good smith.
The weapon in 1929 should have a flat (butter-knife) bolt strait down with no rear tilt.
Does it have Steyr on the left side of the receiver?
Does it have any British proofs,many of these guns were "customized" or "remanufactured" in Britain.
Many were single trigger, especially the Brits.

Picture would certainly be helpful.