My understanding of cotter pins is, when properly installed, they take no rotational load at all. Their function is to apply enough pressure by wedging the crank against the axle to make the effort to overcome friction between the axle shaft and the bores in the cranks greater than the effort needed to turn the chainwheel. (By the way, the left crank is the only one to send power through the axle: if you had only the drive crank, there would be no torsional load on the axle, only bending loads.) If the pedalling torque is transferred to the shaft of the cotter pin, it will deform and get loose very rapidly. Consequently, it doesn't matter which way they point when installed: as long as they point in opposite directions and have the same taper, the cranks will be 180 degrees to each other.
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Michael Shiffer
EuroMeccanica, Inc.
114 Pearl Street
Mount Vernon, NY 10550
(914) 668-1300
euromeccanicany.com