Hi Derek! I've been looking through my books and other resources, as others have said, it was normally the outer guns that would have been removed keeping the weight more towards the inside of the wings. Also looks like they kept the same gun cover under the wing, doubt they would have gone through the expense to retool. Still looking for any good, clear photos.
Do you have the P-40 manuals? If you don't, I could even e-mail them to you or throw them on my server for you to download.
I don't know if you have seen this video, it's been awhile since I have watched it so I don't remember if they show the gun area, but maybe it will be of help for anything else you would want to do for the aircraft.
http://www.zenoswarbirdvideos.com/P-40.html