When military 1911 pistols were rebuilt, serial numbers were NOT erased and a different number stamped.
When a 1911 was rebuilt, the arsenal doing the rebuild stamped a mark on the left side of the frame, indicating the arsenal that did the work.
As example, Augusta Arsenal rebuilds are stamped with an "AA" mark, Red River would be "RRA" etc.
They DID NOT alter or erase original serial numbers.
The reason the numbers were defaced is almost certainly because the gun was stolen from the military and someone thought erasing the serial number would prevent it being detected as stolen. Why someone then stamped another number on it is a mystery.
What you have is an ILLEGAL GUN. Federal law states in no uncertain terms that a firearm that's had the serial number defaced or altered is a FELONY crime to possess.
This is no BS. This is a felony in every state and under Federal law.
What you can do is request the BATF to issue a new serial number and have it stamped on the frame to make it legal again.
This is even easier if you can still determine what the original number was.