Now, you've done it

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The (up to) 23" barrel for an M1903 is the first 'option' listed. Other variations of the stock were also listed, but no removable comb.

Here are full images of the three pages (50, 51, 52) of Mannlicher Schoenauer from the 1939 Stoeger.
Note the barrel lengths and that the M1903, M1905, M1908, M1910 are only offered as carbines (stutzen).
The "Mannlicher Schoenauer High Velocity Rifle with sporter half stock", however, could be ordered with "Full stock in rifles which normally have half stock" from the options list for an additional $10.
The Takedown is "only made in the sporter half stock model, not in the carbine, and on special order only."

Does "special order" and "regularly available in the following calibers" (the High Velocity) infer that the M1903, 05, 08, 10 could still be 'special ordered' as halfstock or takedown as late as 1939? Would it be possible to import Austrian rifles to the U.S. after the Anschluss of March, 1938?

Spares of part #2 above, Foresight, are what is stored in the removable grip cap on MS so equipped.