My best guess is 1970, from memories of the first GE folio catalog I got that year. IIRC it was the next year, that GE trashed blue speckled Plastisol for "Celery" and "Avocado" which is the finish on the machines in the brochure above. Also, if that last letter in the model number is an "L" that would be 1970. The model below is from 1970 and is one step down from yours.

Your machine probably actually pre-dates Peteski's brochure because the comparable model in the brochure is SD660 and yours is a SC660.  And The cycle description had in the brochure said Power Scrub (cycle name) vs. yours saying Pots Pans as well as yours has mini wash (capitalizing on the mini-basket fame) and Peter's has short wash.  A neighbor at our lake house had htis very model and their house was built like in 1970 or 1970 at the very latest, could have been as far back as late 1969.   I doubt your PotsPans cycle would be as long as the Power Scrub cycle. Your button cycle names is a harbinger back to the mid-to-late 1960s GE dishwasher.  This was probably the last year before they introduced the PotScrubber line. 

I had a 1986 PotScrubber with the rapid advance timer.  Energy Saver cycle was 36 minutes.  Light wash was 44 to 50 minutes long.  Normal wassh increased time by another 12 minutes.  PotScrubberr was 83 to 88 minutes long.  Those times do not include the 30 minute dry period.