Since the front bumpers of the 4104, 4106 and 4501 are the same, it's entirely possible that 'Hound could have installed an '04 bumper on a Scenic if either one had been in a fender bender and that's all the local HD shop had in inventory at the time. The reverse is also true.
I think, but am not positive, that the optional fog lights (which necessitated the "holy" front bumper) were not ordered by most of the Greyhound divisions on their Scenics. It was a semi-popular option on '04s and '06s with other carriers, tho. . .
FWIW & HTH. . .