Raimey, I don't think this rifle was rebarreled, not even the receiver. Only the standard service charge marking was changed, reflecting the 1910 change of powder and load, with proof pressures and ballistics unchanged. Remember, Frankfurt on Oder had it's own proofhouse initially, because of the Collath factory there, but I lack knowledge about it, except it was moved to Spandau sometime before WW1, when?, and closed down following the Versailles treaty. I don't know either when Frankfurt-Spandau changed from gauge to mm.
Mark, your action is a large ring one. It lacks the usual Mauser commercial markings, serial number and others , behind the recoil lug. Here it shows the typical factory internal markings of the government arsenals Spandau, Danzig and Erfurt. As you noted, the firing pin is of the pre-1901 type. The Mauser transitional actions are all small ring ones. Pre-WW1 "surplus" M98 actions were usually not available, everyone wanting to build a 98-action rifle had to buy a commercial action from Mauser first. But I have seen two Suhl-made rifles on cock-on-closing small ring 1896 military test actions, apparently sold as surplus after the end of tests, so IMHO your action had a similar fate. Your bolthandle was certainly altered from the original shape, more likely reforged than replaced.