Lana Turner as Laura Manion?
Whatever the reason Turner left this picture, I just can't imagine her in this part. There is the practical reason that she was at least a decade too old for the part, and she would have looked out of place as the wife of Ben Gazzara. (I know there was less than ten years' difference in their ages, but Gazzara came off younger on film -- he looks mid 20s here -- and Turner by the late 1950s was typecast as a sexy older woman in things like "Peyton Place." In "Imitation of Life," released the same year as "Anatomy of a Murder," she looks 40 though she is officially a year or two younger than that.
The other problem is that though Turner more often than not played sexually aware women, there was nothing "easy" or relaxed about her performances: she always had a sort of tension, and a sense of awareness she was doing something wrong. So the character of Laura as it's played by Lee Remick -- which is presumably as Preminger envisioned it -- I just don't see Turner being able to pull off.
Laura as an aging, bitter woman married to a jealous younger man: that would make this picture something very different from the one we know.