A Squared:
You would have to ask the UK CAA why Atlantic were allowed to operate the L188 without a F/E.
Wunwing:
When I flew in the USA, our company had an ex-Air Canada DC-8 equipped with the extended rails (to the F/O's seat). I think it was a 50-Series and it was used as a Combi. I know George wanted to fly it as a 2-pilot machine but the FAA wouldn't let him.