Perhaps Ken, Bob, or AMFAMAN could comment in more detail, but you're completely overlooking the role of the flight engineer, Bears.
The origin of the third man in the cockpit was as a trained mechanic, not a pilot. They had no more training on landing an aircraft than the flight attendant did.
When I joined AA in the 80's, there were a couple hundred left (all of them senior enough to hold bidlines on the same overwater flights you're so worried about). When the 727's were retired in 1999, there were still a dozen or so left on payroll. A lot of airlines like Kalitta and even ATA who fly to places like West Bumblefuq and Al-Dirtpatch still use PFE's because they're able to sign off logbooks in places where it's unlikely to have a licensed AMT.
Ironically, the reason that mechanics got kicked out of the cockpit was ALPA -- they convinced Eastern's management that pilots could do just as well of a job in monitoring aircraft systems as the FE could. When the FEIA went on strike at Eastern in 1962, ALPA jumped at the chance to take over those jobs (scabbing/raiding the FEIA is one of the key reasons APA decided to split off from ALPA).
Even more ironically, watering down the role of the FE is what prompted the FAA to reconsider the requirement to have a three man crew. Since the FE was an insignificant position as ALPA purported it to be, they chose to certify the DC-9 and 737 as two man cockpits. With that foot in the door, every commercial airframe certified since then has been a two man cockpit.