What story are you talking about in the '70's? His destiny might have been to become Superman, but Jor-El did not send him to Earth for the express purpose of showing humans the way as he is portrayed in Donner's STM. The Superman of the '70's was Superboy as a teenager and became Superboy b/c of his own desire to use his powers for good and through the guidance of his parents, the Kents.
This is from Superman Through the Ages website:
"Once there was a void, when Chaos held sway, until there were spoken the magic words, 'let there be light!' Some called this event 'Genesis.'" Thus begins the earliest piece of this new origin of Superman, as presented in Superman Annual #10. One piece of primal matter formed in that creation somehow took the shape of a sword. That sword floated through space for eons and later came to be known by the strange symbol on its hilt, in millions of languages, on millions of planets, as the "Sword of Superman." The sword is the stuff of legend, resisting the efforts of all who try to capture it, as if sentient, as if waiting for the one being in the universe who is destined to hold it.
Meanwhile, on a planet in the exact center of the Milky Way Galaxy, a race that is almost as old as the universe takes it upon itself to guard the growth of intelligent life on as many planets as possible, first through a corps of robots assigned to protect a small group of planets (the robots would later become known as Manhunters), later with a galaxy spanning batallion of magic ring wielding warriors. Realizing that even immortals can't last forever, the self-styled "Guardians of the Universe" hope someday to turn their task over completely to these Green Lanterns, if only a warrior of such noble proportions can be found who would be capable of leading them (Superman #257).
In a seemingly unrelated event, a race of gaseous beings called the "Sun Thrivers" created a giant red sun by drawing matter from nearby parts of the galaxy. They intended to use this star as a home for themselves as they travelled around the universe. The fate of their original star is unknown. Presumably it was destroyed in some manner, possibly a manner similar to the ultimate fate of this new sun.
Indeed, this sun proved to be an unstable vehicle. The Sun Thrivers compensated for this unbalance by creating planets to orbit their sun. One of these planets, made of incredibly dense matter, was unstable itself. However, the Sun Thrivers managed to hold it together for 10,000 years, long enough for another race of cosmic beings to get some use out of it (Superman #255).
Soon after the creation of this incredible artifact, two space explorers crash landed separately on its surface. Even though they didn't know of each other's existence, they managed to find each other on its gigantic continents. Unable to rebuild their crafts, the two astronauts are forced to make the best of life on the barren planet, with its wispy atmosphere of crimson gases. Coincidentally, the two astronauts turned out to be a male and female of the same species, one named Kryp, the other, Tonn (Superman #238)
These two stranded astronauts turned a world so unfit for life that early generations had to sleep more than half the day and felt more comfortable crawling than walking, into a bustling super scientific civilized world. The weakest died before they could produce children, but the human species displayed its surprising adaptability and evolved to meet the challenge.
The race's physiology was subtly altered, although the outward appearance changed very little. Muscle tissue became denser. Motor reflexes became sharper. Optic capacities widened. The race began expanding out from the low gravity regions around the equator to the upper latitudes. At least, that's the way Elliot Maggin described it in his 1978 novel Superman: Last Son of Krypton.
Central to the history of this evolving planet was an incredible family called "El." Kings, philosophers, scientists, explorers, musicians, and architects all followed one another with bewildering rapidity. It was almost as if someone was watching this family, guiding them, in order to produce an evolutionary masterpiece, a Superman (The Krypton Chronicles).
That someone, most likely, was the aforementioned Guardians of the Universe. For 10,000 years they had manipulated the descendants of Kryp and Tonn until, in Jor-El and Lara, they had created the genetically perfect couple, the couple who would produce the one who would be heir to the Guardians, who would rule the Green Lantern Corps after their passing, Kal-El, the greatest Green Lantern of them all!
Unfortunately, the planet they had chosen for this experiment was unstable and due to self destruct. A Green Lantern named Tomar-Re was dispatched to preserve the planet until Jor-El could build a space ark and escape to found a new colony. This plan, too, came to disaster, as the space villain, Brainiac, stole Jor-El's completed space ark when he shrunk the city of Kandor and placed it in a bottle. Though he fought valiantly, Tomar-Re was only mortal. He could not save Krypton, and so all perished, except for Kal-El, who was rocketed desperately away into space by his father, determined that at least something from Krypton would live on (see Superman #257).
The rocket bearing Krypton's last son landed in Smallville, Maryland (or was it Kansas?) where, with the intercession of the famous scientist, Albert Einstein, who had been contacted by Jor-El for help, the foundling was adopted by the Kents. (This moving the time of Superboy's adventures from the 1930s to the 1960s.)"
Afraid you're wrong about the Kents. They are in the origin that appears on the first two pages of Superman #1, 1939. I'm not looking at Action #1 right now, but they might be in there too. Then the major origin of Superman from Superman # 53 (I think), 1948, Pa Kent even names him on his deathbed. So, the Kents have been there from the beginning, not sure where you heard otherwise. Why else would he be Clark Kent.
If the Kents are not in the Action #1 appearance, you must remember that the story that appeared in Action #1 was incomplete. It was missing the first 6 pages which were included when reprinted in Superman #1, less than a year later I believe. Action #1 does include a brief origin summary, different from the one that is in Superman #1, I think. I'll have to go grab my reprint and check it out.
I'm sorry, I mean the original Siegel and Schuster newspaper strip from January 16, 1939 (before Superman # 1). "The sleeping babe is rescued from the burning spaceship by a passing motorist, and turned over to an orphan asylum...."
Very good question. 
