Welcome to the Forum, jingks
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Seeing that you have a GT, your brother is correct with the stock plugs. Some one else on the Forum with a GT may have other options.
As far as the coil goes, most will tell you it is a waste of money as the stock coil as good as replacements.
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2008 Silver Steel Metallic, Touring, NA, Sirius; Chromed door handles; lower grille; fog light surrounds; chrome front & rear bumpers strips; Airaid air filter; Bassani duals; Modesty Cover; Autolite AP5263 Platinum Plugs (.040); Crane Plug Wires; NAPA Ceramic pads; Blane hood struts; PTeazer Gas, Brake & Foot Rest Pedals, '05 Rear Step Pad, Stainless Door Sills, Llumar tint, "A" Piller chrome; APC Strut Bar