bullcrap. the only real difference between the LA and mag rods are the mag rods are narrower on the little end (1" for the magnum, IIRC). you can't fit a piston designed for a magnum rod on an LA rod w/o narrowing the little end, but you can put an piston designed for an LA rod on a magnum rod. heck, most aftermarket rods are narrower than LA rods
on the little end (and pretty much the same as a mag rod), because the same forgings are used for SBC apps.

a KB362, designed for mag rods will give ~1.2 points less compression than a KB107