There's a fair chance that you have a Mark One Au Lion that some WWII soldier modified.
The Mark One in both American and Au Lion versions were heavily issued early in the war to paratroopers and Rangers, until the supply was exhausted.
It was common for them to modify and customize these knives.
As such, it would have more value as a collectable then if fitted with one of the current, really, really, horrible Chinese replica handles.
The current replicas are so terribly bad such a handle would probably detract from any value.
The Japanese replicas of the 60's and 70's would be much better if you can find one, but I wouldn't use a current handle.
Original WWI Au Lion knife, and a cheesy current Chinese "replica".
Note how the Chinese isn't even remotely like an American or French original, or a Japanese replica: