Need GM Parts Book Interpretation
 

In a 1981 dated GM parts book what does the model Sprint-57 mean?

Taking a guess:

https://i.postimg.cc/bwHMQG1q/screenshot-8356.png

Here is the reason I ask the question. I have these NOS seat belts that have part # 1744480 and 1744481. The only GM reference that popped up was a 1981 GM parts book that said Sprint - 57 with a Model "A". I guess the "A" designation would correspond the Malibu / El camino line. The color indicated in the book was "Firethorn"

The GM boxes are dated 1974 though and the guy I got them from had mostly Corvette stuff.

Do these look familiar to anybody?