I would take it off and blast the paint off, then just start it, you have the other side as a reference, you would be surprised how easy metal is to work with, years ago th gentleman that taught me said "aim small", I got it after he had me hand make a couple trunk gutters, cut your first strip, grind and shape it as best as you can, then tack it in at the easiest side or the one that matches best, then dobble, grind, and tack as you go along, the parts where you can't get the metal to bend perfect, dobble them a bit low, wipe them with the tinning butter, heat them up, add the lead, let them cool and sand it to the shape you want.
That fender is 3 hours as I see it, the picture wont blow up for me so hard to tell, but very fixable...
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16 gauge metal, I often cut the metal out of junk hoods, doors, and fenders I save, sometimes you can get the bend you are looking for for another fender, even though its a different make, model, year, etc. I used a piece of a charger fender to fix a chevelle panel before, an edge I don't have to bend saves me time...
