Don,
I suspect that you are probably correct that it is a parts gun. The reddish color indicates a salt re-blue at an incorrect temperature. The 58404 serial number is also way out of range for a Brazilian contract Luger. Most likely it is a Brazilian receiver placed on a 1906 Commercial frame. If you would like, you can send pictures to
rwood1@elp.rr.com and I will try to give you a more accurate assesment.
Ron