Run from the 780 as fast as possible! This fact should be a sticky...every one of those is waiting to break. It's not even a "oh you get a lemon here and there" deal, EVERY one is going to break with use. Kind of a shame because it's a neat looking gun IMO.
As for parts, no they do not interchange. You "may" be able to get a stock to interchange with some finagling, but that's it. They're based of some mystery shotgun that I've never encountered, hell they may even be based off a pump action rifle. The reciever is noticeably smaller than most shotgun recievers.