Welcome!
Wait one ... there is no inletting for the sling, so not a K98k but another flavor of Mauser (at least, I have never seen a K98k that wasn't cut for the sling). Hmmm ... I will now head downstairs to locate my stock like that. It is an from a WWI Oberndorf Mauser 98, but I cannot for the life of me recall if it sported the takedown rivet and no cut like yours ...
EDIT: Whoa! Long time since I looked at that pup. No takedown rivet ... a space that housed a unit ID disc, instead ... and no sling cut, but a sling swivel underneath just aft the grip bump.
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One time I "rebuilt" a Wz-29 (a Polish flavor of the large-ring 7,92x57 Mauser) by starting with a
beeeooootiful barreled receiver + matching bolt that I acquired thru sheer serendipity.
That left me with the difficult task of finding correct "furniture" for the thing. I lucked out twice because Richard at
Springfield Sporters had what I needed in-stock but unlisted and sent it to me for a pittance.
It usually is not that easy , though ... but it, for
me, it has been, on several occasions, fun.
Enjoy!