BSW, it would have been used by the Austrian postwar army for whatever it would fit on with that button stud arrangement I reckon, which is about everything except and slotted K98k stock. I'm sure they used them on MP.40s as well. That is absolutely what that sling is. This one wasn't faked/modified for a K98k so good as they simply added a hole closer to the end. They can be cut to K98k length, trimmed on the end to a point and a hole added in the back and they are perfect size. Again, original Kar.98k and MP.40 slings are 120 cm = 47" and these are around 142 cm = about 55", measured from tip to buckle end.
Here is one that is painted/unissued. I've got a couple of these. I use them on my shooters. They are great high quality slings, just postwar, and I much prefer them to repros, which cost about the same.