Here are a series of pics showing how I attach a shoulder strap to the plains style side quiver. This attachment has other applications too.
First showing the components of this attachment method. I am using 3 holes on the osage buttons but 4 holes works well also. feed the thong through the two holes in the osage button from front to back, then through the holes in the strap(these holes are the adjustment for the strap length),go around the stiffener rod on the quiver and back through the holes in the strap above the previous holes. Now bring the two thong ends through the single hole(can also be done with 2 holes here), draw up tight and tuck the ends through the original thong loop in the button. Now pull everything up tight and you are good to go.
I made the pouch removable also and it is just tied to the stiffener rod with 2 thongs. This way the strap and pouch can be removed switched to the other side of the quiver for ambidextrous usage.