Forth, 50 bytes

Though FORTH-79 is the earliest standardized version, the language was in development starting in 1968, and was usable on the IBM 1130. It was used on other systems as well before 1977 came around. I may do a bit more research to ensure these words were all available, but I'm fairly certain this is basic enough to have existed by then. These were all available by FORTH-79, for sure.

Loops forever, waiting 6420000 milliseconds between string printing. No newline is printed.

: F 0 1 DO 6420000 MS ." 4 8 15 16 23 42" LOOP ; F