J294 is just an internal Los Angeles assembly plant processing code. Car 294 in batch J which means nothing.
Every car/tuck (Chevy-Pontiac etc) built at LA GMAD during this period (1967+- to 1970+) will have a similar code A001 to Z999, repeating over and over.
There is nothing on this tag that confirm anything other that date built, paint and trim colors.