I think they use the same exact cars for the Santa Train every year. They're from a special pool of Blue Line 2600s designated for work service (like the candy-striped 2400s everywhere else) and equipped with jumpers for controlling the air brakes on flat cars. Also I'm sure some other electrical modifications (in the low voltage circuit) have been made so they have places to plug in all the lights.
That old car might be worth money!