Does anyone know who made this Vintage Mountain Bike Frame?

Well, you certainly got your money's worth. It would be hard to tell who made the frame, and it doesn't really matter. It appears to be a pretty standard TIG welded steel frame of good quality. The components are also good quality. The shifters, although they are friction, are Suntour power shifters, one of the best designs ever, I had a set on a bike I used for years for commuting with never a problem. Those older non suspension mountain bikes are very versatile. They make good commuters, and can even be converted for use as touring bikes. Very rugged and simple to repair. This will make a great winter bike