Front,, to get low protection for that frame & engine.
Im not sure it would be a bit more work to build from scratch what I see in my head. Im thinking it would be just too hard to modify the existing fender, But then,, I know I dont have what it takes to shape a fender out.

IDK,, I guess if I had a mig Id look at a piece of the heaviest walled exhaust pipe I could find & have a piece bent in a long radius to fit the tire, split it & open it up. 2.5 " pipe opened up would make almost 8" of
fender. Thats plenty of metal to find a shape in..

MIte have to have some flat sheet to add to it for supports & maybe fill part of the radius, but I think I could build a fender from that .