The Floating Drydocks Gato-class plan book has numerous photos and line drawings of Gato/Balao subs.
There are several pictures shot from the lookout station toward the bow which show boxes. There are some line drawings which show the conning tower structural parts.
http://floatingdrydock.com/update.htm
This is an indispensible reference for detailing a Gato/Balao. I have the hardcopy version. Tom Walkowiak at FD has recently released an updated electronic book version in PDF format on a CD. It is supposed to contain more information than the hardcopy version, which will make it a more valuable resource. I have Tom's Cannon/Edsall, Buckley, Sumner/Gearing, and Admirable class eBooks an d they are great