Do you really plan to convert everything to id tech 4? Sounds like a very difficult thing (and OA devs stated that switching to another engine would have break Q3 stuff compatibilty, which is one of OA goals)....
However, if you are searching for OA sources, give a look to the links here:
(
DO NOT LINK) h t t p s : / / openarena . wikia . com/wiki/Main_Page#Coding-wise_.26_other_stuff
Most updated gamecode ad engine sources should be on github:
https://github.com/OpenArena/While other stuff (images, maps, etc.) should be in the SVN... not sure if this one is updated:
http://openarena.ws/svn/ (its extremely simple web interface does not show any date or other info about the files... maybe
DO NOT LINK[/b]) h t t p s : / / openarena . wikia . com/wiki/Subversion]using a subversion software gives more infos?)
There was another svn link (which used to show more informations):
http://www.mancubus.net/svn/openarena/ but at the moment it says 404 error (not found)... I have no idea what happened to it. Maybe Sago or Fromhell know.