The 3.0L valve covers did not switch to plastic till model year 2000. 2.5L valve covers are still aluminum.
All 2.5L LH valve covers will have an extra section at the back of the head for the Rear Accessory Drive. This was added in model year 2001 to the 3.0L in the Escape, Tribute, and Taurus only, not Lincoln LS.
1996-1999 3.0L and 2.5L share the same RH valve cover.
