Ford 2003 Mustang Workshop Manual page 1563

33. Install the LH timing chain on the camshaft sprocket, aligning the copper (marked) link with the
timing marks on the sprocket.
34. NOTE: The LH timing chain tensioner arm has a bump near the dowel hole for identification.
Position the LH timing chain tensioner arm on the dowel pin and install the LH timing chain
tensioner.
35. Remove the retaining clip from the LH timing chain tensioner.