The wheel to wheel step bars on long bed trucks will be longer so the step bar fillers will not fit properly as they will not be long enough. There would be a gap between the end of the filler and where the board ends.
The mounting brackets on the wheel to wheel step bars for the 8' bed are in different locations than they would be with a 6'9" bed. The fillers will not work with a truck with the 8' for this reason. Since the fillers are 1 piece and custom fit the mounting locations will not match up between the body styles.
They are still available. Here are the fillers for the cab length step bars with the Ford oval and Super Duty logo,
Polished stainless finish: https://www.sharptruck.com/gatorgear-ford-oem-step-bar-fillers-black-ford-oval-supercrew-crew-w-oem-straight-bars-gg758499
Black Anodized finish: https://www.sharptruck.com/gatorgear-ford-super-duty-logo-oem-step-bar-fillers-black-anodized-aluminum
Truck Hardware does not make these for the 2005 Excursion and unfortunately they do not have plans to make them. With the custom fit nature of the fillers there is not something i could recommend that would fit either.