The Chowchilla incident happened in 1978. "The Mod Squad" was off the air long before that.
That's right -- CHOWchilla, not CHINchilla, as I stupidly thought!! No wonder I couldn't find anything under "Chinchilla bus buried" when I googled! *sheesh* Anyway, that Mod Squad episode was so much like the real incident that it seemed beyond coincidence. I figured that the guys who pulled that off must have seen a rerun of that Mod Squad and gotten the idea from it.