Looks like a classic mixmaster. Probably not a re-weld, as mentioned, it looks too good. I agree that if one could see the receiver ring, it might say "M1icon". It's very easy to alter an M2 marked receiver (as this Inland S/N indicates it was). Drill out the "2", fill with a small puddle weld, either stick, flux core or TIG, file and sand down with care, and stamp with a "1" using readily available metal stamps. Then re-park the whole thing. As I understand it, that is highly illegal to do, so don't do it. However, not many folks would know this S/N came out of the factory as an M2.