buckstix,
First, re-read the comments for your other rifle on Nitro Express forum. What you seem to have is another pre-mod 98, this one #27 and may be the smallest number known. The small bolt hold down was likely added by Sauer, because the early transitional actions lacked the spring-loaded plunger on the left side of the bolt shroud. If that is not enough, the Imperial eagle acceptance stamp on the top right-hand side of the barrel likely means it was used in early WW1 as a sniper rifle. I say this because if this stamp was placed during the pre- acceptance test of mod 98 actions, it would not be on an octagonal, but round barrel. If it is what I think it is, you should find evidence of a plaque having been attached to the lower right side of the buttstock. There may be evidence, also, of a unit stamp on the stock. The stamp on mine is pretty clear, but the plaque screw (or nail) holes have been filled and you have to look closely to see them. The plaque was a caution against using any ammunition except that having .318" bullets. It has been a long time since 1914 and a lot of things could have happened to the stock. Since you are interested in mounting a scope, I would advise against doing it in a way that modifies the rifle. The German Gun Collectors Association's technical editor, Axel Eichendorff wrote an article in WAIDMANNSHEIL, Issue #47, Winter 2011, concerning these rifles. If you don't have a copy, I recommend you obtain one and read it, you will find it interesting. I will study the photos again tomorrow and inform you of anything else I find.
Mike