IIRC the longest that we have continued a B744 following an IFSD was 6 hours! Totally legally under the FAR's as quoted above
Indeed so, it most certainly is.
The same is true for my three engine airplane.
However, we should remember that these regulations were originally designed for the
enroute IFSD situation.
To apply them to a takeoff situation, followed by a very long overwater sector, with limited enroute alternates is, in my opinion, stretching the (legal) regulations just a tad thin.