well if he not the 4th there here another idea. jsut somehting i jsut figured out i think....

the sealing of the death gods takes the user soul and in teh end the 2 souls are bended together in a entral fight(lest that close to what the 3rd said) so i'm thinking waht if the "gate" that holding the demon fox in mihgt be the 4th soul power keeping it contained ? that might explain while nartuo can learn so high moves so "easy" compaired to others so fast liek teh regensen and his shadow clone skill.

shadow clone skill was in the forbbin seal scroll(thought we seen a few other used of this skill) i would guess in there 6 rank system it be close to 4 to learn this one

regensan - a rank 2 of 6 skill high one and took the 4th a while to learn and master it last step, yet naruto learn the final part in a weeks time(from teh bet so might be more like a week and a few days cuase of travel)

this might be why he seem to ahve a knack of some skill like one the 4th sued. just a idea i like to keep poeepl guessing and think things over in a new light :-)