Well, he's supposed to be very tall and is right around the physical age where he'd be hitting growth spurts and such, so probably a couple inches. Not much, but when you're 4'7", every bit counts.

It's a spiritual thing, not a natural thing, so I don't think they could interact/switch if everything supernatural is gone. It's sort of like the set up with Ichigo and Hichigo, only they were originally separate beings.