Interesting about the 313 knots as a windshield issue.
The L1011's that were on the UK civil register had this limitation, below 8000 feet, as I recall....however it was not an FAA requirement.
Of course, the Brits required other changes as well...scarfed pitot tubes, lower Mmo (M.88) among others, and most distressing of all, you could not select CWS with an autopilot on the ground for takeoff, quite unlike the FAA certified aeroplanes.
Also, further to Vmo and Vne, under present FAA certification rules, if a piston powered aeroplane was re-engined with turbopropellor engines, the previous Vne would go away, and the old piston Vno would then become Vmo on the 'new' turbine aeroplane.