depends on which truck you talking about from the movie, they had 5 blue mule's for the movie and some scene's it was a different truck, Filming took place in later 1974 and early 1975
the one mainly used was a 1974 Ford WT-9000 used for the filming in 1974,
Truck #2 was a 1975 Ford WT-9000 used for the filming in 1975, while Truck #1 when to truck stop, shows and behind the scene's picture's the photo on the VCR with Jan Michael Vincent standing in front of it with a gun and etc. to advertise for the movie
Truck #3 was a 1972 Ford W-9000 Universal Studio's acquired it from Ford Factories as left over, Ford Factories had it as a show truck to advertise for it's model "the W and WT-9000"
Truck #4 was a 1973 Ford W-9000 it was a stunt truck and scrapped back in 1976
Truck #5 was only used in 2 scenen's of the movie it was a Modified WT-9000, when it was actually a 1965 Ford W-1000, the only s scene's was part of the final cause this was the truck used for the jump, they switched to this truck in the scene right when they started to fire there guns in the final scene, before that for the night scene it was Truck #4 and the other scene it was used in is when the truck had paint marks all over it with the snake in the cab, this truck was scrapped right after filming in 1975
Here is my build of the "Blue Mule" from White Line Fever, I still have to put the Mule Symbols too, But I am just going to get a new cab and use JBot's decals he sent me,anyway here are some links to it