Looking closer at Gew98s I believe you are correct. This could be my answer to the trigger guard as well.Looks like the floorplate is off a Gew98, or at the very least an imperial-proofed rifle.
Here, hastily googled but you can see what I'm talking about. The sling is attached to the trigger guard, not the sling swivel on the buttstock.The trigger guard is off a Gew98 as well. That hole is for the older quick-detach style rear sling swivels that you see on Gew88s and Gew98s . I believe it was a parade position for the sling.