There are two different oil rails that Navistar used for the 6.0 Powerstroke and VT365 engines.
From the first one produced until 9/29/2003, what we refer to as 1st generation, they used a single round oil rail (bottom of picture).
After 9/29/2003 they switched to the wider, webbed design (top in picture), 2nd generation. When building a replacement engine, we must install the correct components to match your truck.
WARNING: You can not always go by the production date on the vehicle.
Some F-series trucks built in 10/2003 have the smaller oil rail and a large majority of the Excursions built after that date have the 1st generation oil tube. Engines that were installed in the E-series trucks also have the 1st generation oil rails until the 2005 model year trucks were being built. At that point, the E-series switched over to the 2nd generation oil rail while the Excursions continued to use the 1st generation tube until Navistar ran out of them at which time, they switched to the 2nd generation.
Confused yet? Don't worry, if we are in doubt when you order an engine, we will ask your mechanic for a visual confirmation.
We Keep You Strokin'