I decided I'll have hat channel made to stack on the existing stuff for the roof raise. Now I have to figure out how much to order. I remembered today that my phone might take panoramic photos (hadn't ever tried before) and got it figured out. Unfortunately the focus isn't good, but it's good enough to mark up the walls! Shown below are the left and right walls all the way from front to back. Markings are as follows:
Yellow arrows denote existing channels which I'll un-bolt and un-rivet at the top; I'll add extension channel at their tops rather than cutting them mid-height and having two splices in each.
Green lines denote locations where I'll remove the existing short channel and replace with new full-height channel (including the height of the raise).
Red lines denote locations where I'll cut existing channel. There are only two on each side, above the front windows. These I'll probably still un-bolt and un-rivet at the top (because I'll be replacing the exterior skin which is held by those same rivets), but the piece of removed channel can be shortened and re-installed.
Blue lines denote the outline of future window locations. The two at the front on each side will be re-installed original windows. At the rear on each side there are stacks of three short windows. Bunk beds for the kids will go in that area with a window for each (hoping I can find six small-ish matching windows at a good price!). Around the middle on the left is one window that will be above/near the sink. I might re-use the original driver's window here.. but probably not.
Originally I had thought to re-install one original window on each side in the bunk bed area because they could be used for emergency exits. But having a bed installed across the middle of the window kind of ruins that idea, and the window isn't tall enough for all three bed occupants to have a view. Instead, I think I'll install one of those emergency-exit-capable original windows in the rear wall over the engine. The space over the engine will be my bedroom. I guess that if there were an engine fire the bed-area occupants could flee mid-ship to the door, and if there were a fire more mid-ship or at the rear axle anybody in the bed area could exit through that rear window. Does that seem reasonable? The four original windows to be installed at the front also are emergency-exit ready.