Simon, I can understand what you mean about the shock finding out that the hi-press lines might be flexible hose wrapped with spiralled metal rather than tubing. I've wondered a few times in similar applications (not submarines) where I've seen flexible instead of tube.
Of course, flexible IS much easier and faster to install, as I found out when I changed the fuel lines on my boat. No joinery at bends and it only took minutes, rather than hours, to feed it through all the bulkheads and openings from one place to another. I might have needed expert help to install tubing but flexible I could do all the work myself.
As for the boats in the pic, They do look like VIIC's, not VIIC/41's, mainly because of the 88mm bases and the ready ammunition cannisters for same.
However, I'd think the basic substructure of ribs, bulkheads and deck frames would be the same for either version. It wouldn't be complete redesign for that aspect. The lower wintergarden is a structure built up on top of the deck so wouldn't necessarily have a lot of different structure underneath it. In fact, since some boats had the lower platform added on after a few patrols (U-711 that I'm building is one such boat), it's likely that no substructure was needed.
A question though. In the centre boat in the picture, there seems to be a flat base that the felxible lines are going in to. Any ideas what that is? I don't see where it matches any structure on top of the finished boat.