Thanks for the great pics!! Glad you managed to land it. Always nice to see a good piece go to a good home.
Here are pics of my jacket and observations:
Mine had no arm badging or wings. It's impossible to remove such things from a leather jacket without leaving very visible stitch holes. Which means mine never had them at all.
Unfortunately mine has no way of dating it either.
Shoulder rank for BGS is pretty straight forward. It is held down by a sewn on button near the lapel and a small loop near the shoulder seam. Just like the camouflage jackets. You should be able to see evidence of the buttons having been there if you look close enough. If you can see no signs then I would be suspicious there was no rank on it. But I don't know how to explain the small holes by the shoulder seam, therefore I'm guessing you will see signs. Look on both the exterior and interior (sometimes they were sewn through liners, sometimes not).