Two similar/relevant cases, but not the same.
Case 1) Schultz & Larsen M69 match rifle. Heavy 6.5x55 S&L barrel on an original Gew.98 action. No. 39xx with no series letter. I.e. first series of that year. All parts matching. Even the follower has a Prussian proof mark and the last two figures of the number. Refinished (parkerized) by S&L. All number, stamps etc clear, as on the Gew88. But no trace of the original crest/arsenal mark+date on the barrel ring. So, if done professionally, it is possible to refinish a rifle so that you cannot see any traces of the origin marks. Like the Gew.88 in this thread.
Case 2) M1896 SwedishMauser / Carl Gustaf production, also in 6,5x55. Dinged wood, but professional refinishing of the metal. The giveaway (as in the case of the Gew.88) is the discrepancy between the wear/scratches etc on the wood and the metal.
I do not think that arsenals, like Amberg or Danzig, produced "unlabelled" actions. Arsenal rifles were part of military procurement, and apart from possible "lunchbox specials", were marked accordingly. But Mauser itself certainly did produce commercial actions for hunting rifles. In the case of the Gew.88 in this thread, I still thinky that it was a normal military rifle that was simply converted to a rimmed case for use by a hunter, and the simplest conversion would have been to the 8x57 IR. Although, as jmoore points out, other chambering are conceivable. We will all know a bit more if the chamber is cast and the bore measured as suggested in my previous contribution.
Patrick