For early in the war, I'd actually remove all the AA guns and have, perhaps, two deck guns as aircraft weren't seen as a significant mid-ocean ASW threat (and weren't until 1942-ish). Maybe reduce the size of the sail or dirty up the fittings of the ship as the early boats weren't as clean as the later boats. Maybe draw inspiration from some of the interwar Italian or British boats? Go with fewer masts and nothing that resembles a radar. Add a sawtooth mine cable cutter to the prow?
Just thoughts.
Paul