I would guess the inlets wouldn't care since they see fue pump pressure anyway (unless it's a gravity-fed Model A Ford or such).
But, in the stock application (2-liter Pinto for example) the carbs are mounted as Langdon recommends. Then when you accelerate, fuel would slosh TOWARD the jets and boosters, just when that would be helpful, for initial response off the line.
If you mount the carbs backwards to that, fuel would slosh AWAY from the jets/boosters on acceleration, which might cause hesitation on launch.
Now, on the big dual-quad Holley Fords, the carbs are mounted "backwards" and this is not a problem, so you might get away with it on the Carter/Weber. Or not. Maybe Langdon has tried it both ways or maybe just playing it safe and advising to install them so the fuel sloshes toward the jets/boosters. Ask!