Maybe RJ can find out something about it from the Greyhound repository.
Well, yes & no. . .
I don't show 5638 as a number assigned to a 4104 by one of the Greyhound ("e" not "a") divisions when new
. The closest I come is 5445 belonging to Pennsylvania GL, then 5700 @ Northland GL.
It isn't unusual to GL to reassign coach numbers when the fleet is repositioned. All you have to do is look at the Scenics - some had 4/5 different fleet numbers during their Hound career. Add to that mix the consolidation of various divisions over the years, and tracking becomes much more of a challenge.
However, it definitely is an ex-GL car. Give-aways are the low-mount driver's mirror, the fleet number placement, the running dog breastplate, and the large flat panel between the headlights for multiple state license plates.
Now if Mr Asip or one of the other band members can come up with an old vehicle registration or similar with the VIN, then I can come up with which GL division originally purchased the coach from GM.
1955 PD 4104-1522 has moved to her new home from Lincoln, Montana where she was purchased to Saratoga Springs, NY.
This coach has an interesting history. It was originally purchased in May of 1955 as fleet number A-5509 by American Buslines, HQ'd in Lincoln, NE. American was the third (and smallest) of the transcontinental bus companies back then, behind Hound and Trailways. Of course, they're just a memory now. . .
FWIW & HTH. . .