The BATFE subscribes to “once a machine gun, always a machine gun.”
In this case, it is highly unlikely any run of the mill agent would notice that (one) there is no model designation on the receiver and (two) the serial number is in the M2 range.
However, considering it is not functionally a machine gun, I have no idea why someone would feel compelled to risk it. I value my other firearms far too highly to risk them being taken away for something as silly as possessing this unregistered machine gun.