I have assembled a number of pictures of various VG1-5 rifles and there slings from the internet and ones that I have taken. These are the internet pictures.
A closer look at the sling.
This is the only picture that I have ever seen with a rear swivel on the sling.
Here is a close up of the sling and swivel.
Another close up of this sling.
These are the rifles that I have photographed.
A couple of close ups.
All the slings look to be a course weave material but of different color lots. Using this as my bases I think I am going with the first version of sling material. I am also thinking about using the swivel as a rear attachment for the sling.
Of the three sling material available I happen to think the first one is closest.
Once again number 1.
You should definetly use a swivel, but with some provisions on the sling that it can be removed from the swivel.This looks fixed/sewed- thus being in function very much like the crude nailed one; just not gonna wear/snap that soon.
Nailed type canvas to steel connection is by far the weakest spot- maybe it subtly shows another last ditch purpose of the rifle (this small detail tells such a great and tragic story); its volksturm user is gonna be long gone/dead before sling snaps max. 2-3 months after the rifle was issued, from regular everyday use and shoulder carry.
Perhaps on the end of the sling you could have something like “alice” harness type snap hooks, that would fix on the swivel.