So what's involved in converting my EF GLi wagon's diff to 3.45 or similar ratio?

After this thread (http://fordmods.com/forums/viewtopic.php?t=8224), swaping entire assemblies isn't really an option, waggin suggested changing the centers or gears, what's involved with that? is it a job i can do or for the pro's?

Now that the cam's in fianlly, this is the next mod!