Differences between automotive & airplane engines

The length of tube doesn't affect the mixture distribution.
The length of manifold immediately after the carbe and before the
divisions to the various cylinders does affect it,....

These tubes are about as wide as manifolds - so should have the same
as your effect "length of manifold after carb(e) and before divisions".
Have you actually seen a working Franklin 6A-350?

and in most of these
engines the intake divides within a couple of inches of the carb. Fuel
spraying from the main nozzle hits the throttle plate at anything less
than full throttle and is deflected to one side or another, striking
the manifold wall and clinging to it, so that cylinders that feed from
that side get more fuel than others.

The throttle plate rotates perpendicular to the engine line, so fuel
should
get deflected symmetrically to both sides and not to one side.
Its really a fairly symmetrical arrangement. Probably not as
good a fuel injection but pretty good as far as carbs go.