1-1/4 sling for a crew served? that all kinds of don't jive. All the hardware looks right to be approximately a korean war era sling. Instead of the tail that goes in the middle being a foot long, it's more like six inches, and ends in another hook. other than that it's just like an M1907.
My buddy ran it past a military historian, who shrugged.
I could post a pic, but other than having an extra hook, it's very similar to the 1907.