Another clue for a cut down stock could be the internal cuts in the cleaning rod channel. Nearly all German gewehr-length stocks (martial and commercial) had routed areas in the forend.
The practice of shimming is prevalent in several militaries that I can think of off-hand. I've seen US, Finnish, Swiss, and Swedish rifles that had shimming done either to the hand guard or under the action. Almost always done to enhance accuracy, though sometimes to prevent rattle.
The Finns and the Swiss went so far as to include sliding aluminum sleeves at the forward stock/handguard/barrel area on some of their rifles.
Some cool spare/armorer parts on the subject rifle. Esoteric question, is the ejector/bolt stop marked in any other way than the serial? I have seen several with armorer markings. All were marked '237' or 'S/42' on the front leading edge.