> took a loooong time for Boeing to convince the FAA that a twin engine jet was safer than a 4 engine for ocean crossings

I don't believe they convinced the FAA twin is safer, just that it meets the necessary safety margins. Airlines want them to meet that regulation for fuel efficiency, but I'd want a source that they're actually safe-er, instead of simply safe enough

Not necessarily safer but safe enough. A modern 4 engine jet should still be safer than the 2 engine equivalent