> Standard US freight envelope doesn't even fit on the standard US freight line, famously there are tunnels and bridges in the East that prevent Superliner and other double-stack cars from getting into New York and other places.

The standard US freight envelope probably counts as Plate C, which is 10'8" wide by 15'6" above the rail. Plate H is the standard for double-stacked containers, which pushes the height to 20'2".

(The part of the loading gauge that I'd be most concerned about is actually the width of the cars at the bottom of the carbody--passenger cars tend to be somewhat narrower than standard boxcar, and given a desire to minimize the platform gap, I'd think there's a decent chance that most freight would strike the platform.)