If i were to cut my spare set of plastics id use an angle grinder or jig saw. First i'd tape a line of where i want them trimmed then start cutting and use a flapper disc for smooth out the edges. I got my quad with the fronts already trimmed so im not sure how the prev owner had them done.
I wanna clean the back of the fenders up I just squared them but don't like it thought about the 366 cut but not sure I wanna go that short or that look