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The easiest way to tell is that the 550 has the wider and narrower intake in the front and alloys that are rounded on the edges. The 575's intake is much taller and is notably narrower; the wheels look more like the 'modular' style wheels. On the back, there's a 575M badge in italics on the 575 - which is an easy give away . Also, if it has F1 transmission, it's a 575.
Very easy. Exteriors: Front bumper (575M, no fog lights but xenon lights), different wheels, 2004 model year has rear badge Interior: quite different, more modern on 575M. From the rear look the same
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