WARNING: This page is about a different car, the 2004 Mercury Mountaineer and 2004 Ford Explorer. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Identifying Special Tool
Courtesy of FORD MOTOR CO.
Place a straight edge across the exhaust manifold flanges and check for warping with a feeler gauge.
Fig 2: Placing Straight Edge Across Exhaust Manifold Flanges