Not Actually TOD: This doesn't fit the true sense of BK's wanting to hear of our favorite actors/actresses who were "backbones" in films of the 60s or 70s, but I would be remiss if I didn't single out Catherine Burns as one of my favorite actresses from the late 60s-early 70s. She scored a supporting actress Oscar nomination for her role as Rhoda in "Last Summer" alongside Richard Thomas, Barbara Hershey and Bruce Davison., and she was totally wonderful in Hal Wallis' "Red Sky At Morning."
In both of those films, she more than held her own with Thomas. In "Red Sky", Desi Arnaz Jr. was also very good. Richard Thomas had made a strong impression on me in the Paul Newman-Joanne Woodward-Robert Wagner film "Winning". He played Woodward's son, and he had a wonderful scene with Newman in which he got inebriated (on very little alcohol). Those three films, plus a very-little-seen film called "Cactus in the Snow" are the only "films" in which I've seen Thomas. He, of course, went into "The Waltons" and became part of TV history. I really thought he was one of the finest actors of his generation. His random appearances on TV now annoy me a great deal as he's always cast as someone just a bit "off", or someone undeserving of his wife or girlfriend or job, etc.