I picked this NOS P 37 (I believe) pack a few years ago and finally had a chance to use it the other day and I have to say, it's really handy. Anyone help on IDing it for for sure? I'd like to make a few of these with slight mods to them and wanted to find an outlet for the brass hardware. I've seen some that sell a few sets, but the prices are really high. What and how are those two wide straps at the top used? I assume for larger shoulder straps? Any other info on this cool bag is welcome.