IABL, I just received this book:
http://www.amazon.com/Vom-Turmsehroh.../dp/3813209318
And it has pictures of how the WW1 periscopes looked like, lots of technical detail, and even diagrams of the reticles
When the time comes and you get busy with the GUI and the interiors, it will be a pleasure for me to collaborate with you and do the part of the optics if you are interested