I wouldnt be a huge fan of just riveting on arches for the sake of it, whatever option is decided upon they will be smoothed and made into the body shape.
Over here in ireland it is next to impossible to get aftermarket parts for the idea i have currently everything has come from America, is there anyone uk based selling the likes of front arches, spoilers etc.
Also looking for a front diffuser and canards for the front bumper.