Calling the FUMO 29 "a problem that needs to be fixed" sounds a bit exaggerated to me. Its position on the conning tower as modelled in game, is historically correct:
If you just don't like it, you can either select in its place the "eagle" radar upgrade (featured by EUF, but not historical), or select the "no radar" option (also featured by EUF, but much more historical) and wait for the next radar upgrade to become available.