I used a very fine tooth blade on a jig saw, took it really slow.. I used the blue painters tape on top and underneath over almost the whole fender. Made a tmplate of what i wanted drew it out over the tape, fine tip marker.
Started a lot lower than the final cut. Basiclly did a few practice cut offs first down lower on the fender.
Worked out really well, a little sand paper on the edge followed with a little paint touch up and your done.
Tried it on another fender with cut off wheels and grinder, not as good.
Good luck
