Wouldn't the same technique that painters use to transfer exact paint patterns (flames and pinstrips too) from one fender to the other fender work? What they do is to use some paper that you can see thru a little and tape it to the first pattern (your left side fender) and then very carefully trace that pattern (your left side fender bracket and fender edges) on to the paper and then you flip the paper over and tape it to the other side (right fender) lining up the fender reference marks doing that will give you the pattern (exact placement) for the other side (your right fender). Make sure you trace the bottom edge and the top edge (next to the body) of the left fender on to the paper or take exact measurements.
Be very careful and make sure you get everything lined up exactly; to be sure I would before making any holes in the right fender I would after tracing the transferred pattern on the right side I would tape the bracket on the right fender and give it a very good eyeball check.
Remember the old saying: “measure twice, cut once”, I would be measuring much more than twice and to make very sure of the placement before moving ahead.
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