Does the Stars yellow Rakshi's back/head combo fit on the body structure of the original Rahkshi?
No. Nowhere for the pinholes to connect
Is it at least the right size to fit snugly over the back piece?
I have not tried, I have the Star Rahkshi, but my friends have a couple 03 Rahkishi. However, I believe the back is too wide, so you'd have to cram the grey back into it. So... maybe?
Yes, it will fit over. You just have to mess with the connection a bit.
Here's an example I found via google search.
Not at all.
Edit: nevermind then