Service even in coach was a treat on transcons. I recall several flights BOS-SFO late 1980's on the stretch DC 8s. Seat pitch in coach was quite roomy. Those large Douglas portholes to enjoy the view. "Coast to coast service" included a good meal, choices frequently included a decently cooked steak or a well crafted cioppino, even a SF native could enjoy.
I too recall the paper upgrades you were sent in the mail, these could be taken to a UA ticket office, now all gone, and redeemed easily for "Conoisseur Class" seats on now extinct routes (most memorably SFO-CDG nonstop in the old 763s.)
Ah for the good old days.....