I have trouble imagining a trip across the Pacific Ocean without a roof.
Back on topic, no two Nagara class ship had a similar bridge. As you noticed, some are blocky, others are curvier. The platform for the quad 13mm were also different, as well as the rangefinders, which went from 12ft on
Yura and
Kinu, all the way to 20 ft on
Abukuma.
Here are some good illustrations detailing the bridge structure after their rebuild (pics found on
http://www.shipmodels.info):
Abukuma
Nagara, Natori, Isuzu
Nagara
Nagara at Shanghai, October 1936
Natori in the King George V drydock at Singapore, April 1943