Unfortunately, you can't tell anything about what TWA or Pan Am was "really like" from this movie, as the cabins were standard Hollywood sets, seen in countless other movies and TV shows. 99.9% of the audience wouldn't notice or care, but very fake-looking to a commercial aviation buff. The seat pitch was probably extra wide on the set so the seats didn't get in the camera's way. To the filmmakers' credit, the flight attendant uniforms were accurate for both TWA and Pan Am, so at least they did a LITTLE research. I was impressed that they got the 1964 and 1967 Pan Am uniforms right (they were slightly different!)
That said, in the 60's and early 70's, seat pitch was somewhat better in coach. I believe it was about 34"-35". The heyday for coach passengers was in the early 70's, when air travel declined so much airlines put in coach lounges to try and win over passengers, even in the 707s! That's also the era United put 5-across in it's transcon/Hawaii DC-8s as shown in the photo. Of course, when traffic rebounded in the mid-70s, the lounges went away, but I don't think seat pitch declined all that much until deregulation. I have an AA seat map brochure from 1979 that still shows a 727-200 with rows up to 26 (They were up to row 30 before MRTC).