Ooookay...
looking at the NSS_Uboat7c.dat and NSS_Uboat7c41.dat files in SuperTurms v6 - the 7c looks like this:
and the 7c41 looks like this:
but when I'm in what Commander and the game show as a 7C41 with STv6 enabled (and no other mods), the deck looks like what you see in the 7c .dat file, not the 7c41 .dat file. Meaning it still looks like a deck that is supposed to have a deck gun fitted by default.
I'm thinking this has something to do with the Turm7c_x_deck.tga files that are embedded in the mod's .dat files for the different turms.