You can change the location and angles of all the weapons in the CSWeapon/xml file:

<Weapon>
<Gun>M61 Vulcan</Gun>
<Shell>Vulcan Bullet</Shell>
<Unlimited>0</Unlimited>
<Station name="Nose" params="0,9,0,0,-0.039,0,1200" />
<Mode name="AUTO" shotrate="100" setshots="0" sequence="1" skipFrm="0" />
<Mode name="X10" shotrate="100" setshots="100" sequence="1" skipFrm="0" />
<DefaultMode>AUTO</DefaultMode>
</Weapon>

These are the settings I changed on the A2A WOP3 Spitfire:

<Station name="Left Wing Outer" params="-4.0,0,-0.5,0,-0.017,0,200" />
<Station name="Left Wing Inner" params="-3.0,0,-0.5,0,-0.017,0,200" />
<Station name="Right Wing Inner" params="3.0,0,-0.5,0,-0.017,0,200" />
<Station name="Right Wing Outer" params="4.0,0,-0.5,0,-0.017,0,200" />

With those changes, I changed the location, and the angle of the guns (M60C) on the wings, so that at a certain range, the lined up with the gun sight reticle.

It took a lot of hard work and messing around (make a change, reload the aircraft, check out the results, then do it all again until I achieved what I want) to get what I wanted, but in the end it was well worth it. :)