Back in my comic book reading days back in the early 1970s, artist Murphy Anderson became the primary inker for Superman artist Curt Swan.
I noticed a peculiarity in the artwork. The backgrounds looked like the work by artist Jack Abel. I wondered then (up until now) if Abel assisted Anderson with the background inking. The page above is a Curt Swan-Murphy Anderson page. The backgrounds look like Abel's.
I went over to the Facebook page devoted to Swan, Curt Swan, Legendary Comic Book Superman and asked if this were so.
I have my answer: