I was actually going to suggest this but, I would normally just fire out of the side of the current C-130 with really big weapons. I'll help start the project up (not by scripting or modeling just getting the pictures and attracting some good add-on makers). Ok I see the weapons used on it.
1-2:The 40 and 105mm cannons, both with highly explosive shells.

3:The 25mm heavy minigun (kind of like mini grenades).

I also see a bombing ability but, lets not get ahead of ourselves.
Now the basic 3D outline...
http://sketchup.google.com/3dwarehouse/details?mid=e27229a5f83b0ac96ece6611a5309fa2&prevstart=0 Sense there aren't any vehicle locking weapons i don't think there should be any flares.
These guidelines serve as a general idea of what the AC-130 gunship should look like.