I see too that the grip straps do not match, and blowing up the picture, I might see a US stamp on the frame.
Unfortunately, that is the first thing faked on these guns. I suspect you have a parts gun here, with a fake US stamp in an attempt to raise value. Nothing that can be proven either way though. The good news is, I see no historical fabric here, so you are free to do what ever you want with it.
Enjoy yourself! Barrels can be found on Gunbroker and Ebay, and some parts sites around the web. I've got a few saved, I"ll take a look and get back. I would not bother trying to find a "Military" barrel. Prices on those could not be justified for this gun. Find a 7.5" first or 2nd generation barrel and have at it!