An original wouldn’t be that easy. To make it look right you’d have to section out the part that’s clearanced because the ridge/lip on the edge follows it. Then epoxy a flat section in and bodywork over the top. I wouldn’t mess with an original ABS one.
Fiberglass would be the same process but the fiberglass work would be easier IMHO. The bodywork would be easier. Maybe that’s just because I know how to work fiberglass and haven’t worked with ABS much.