Sorry to have kept you waiting a year and a half for an answer to your question, Cosmos. By now you've probably forgotten all about posting this question (way back in May last year!) - but your patience is rewarded at last.
Here are the 1970's runaway top best sellers of the decade (at least for the US market - dunno about the British lists, maybe someone else can chip in? Please? Go on. Have a crack.)
Anyhow, I hope this satisfies you for now... Apart from the all time great Kurt Vonnegut, I haven't read any of these novels...not one. Some of them I have only even vaguely heard of. Maybe it's time for me to stop reading so much chick lit in bed?)Top slot on the podium goes to Gore Vidal. He topped the all time best sellers lists for the 1970s - with his novel '1876'.
Breathing down his neck came Sidney Sheldon with 'A Stranger in the Mirror'.
Third place - Aleksandr Solzhenitsyn with 'August 1924'.
Fourth, 'Beggarman, Thief' by Irwin Shaw.
Fifth, the truly great Kurt Vonnegut with 'Breakfast of Champions'.
In sixth place it's Gore Vidal again, this time with his novel 'Burr'.
Then coming up on the rails is 'Captains and the Kings' by Taylor Caldwell.
In ninth slot, James A Michener with 'Centennial'.
Finally, tenth place was snagged by James A Michener again, this time with his novel 'Chesapeake'.
Apart from 'Captains and the Kings' by Taylor Caldwell it's all geezers in the Top 10 - much different from the number of female authors in the list these days.https://www.ranker.com/list/best-selling-novels-of-the-1970_s/bestselling-books