If you have custom gunsights or have associated the existing gunsights differently than how I originally set them up for AH3. Before you run any of these patches updating to 3.04, save off your sights directory. Then copy over all the .txt files after the update because they hold what you mapped to each aircraft or ride in the game for an optical gunsight. It's a good idea to back up your game directories occasionally anyway just in case.
These are the most important in general to backup from time to time or, just before you blow away your install to run a new full install. The sub directory of the "settings" folder called "planes", holds the head position files (hps) for each ride that you custom adjusted your views for.
ah3terr
chconfig
maps
settings
|___planes
sights
skins