The chat box is pretty easy to move. Just open up Halo Custom Edition\content\<game resolution height>log.ksml

Code:
<ksml>
  <head/>
<body>
  <listbox left="5" top="260" width="640" height="130" id="oListbox" 
           textbackground="#00000000" outerborder="#00000000" 
           innerborder="#00000000" shadow="#00000000" highlight="#00000000" 
          textcolor="#ffffffff" font="Arial Narrow-8-bold"    
/>
</body>
</ksml>
Just make that "top" value lower to move the chat box up. The best thing is it gets updated in real time, so just maximize Halo again to see the effects.