Hello propbeanie,
Unfortunately I have no knowledge of 3d editing, and I won't be able to muster the free time for it
. I'm already enjoying working on the campaign files. Looking at the models, I think it's still possible to completely cover up the base of the Kuma bridge with the Sendai one,. Although it would not look quite as real, it wouldn't be that bad, since the AA platform on the Sendai is already larger than in real life.
It is true that there are almost no close up shots of the 5500 ton cruisers during the war itself. The only good one is of Isuzu; otherwise it's distant shots from american aircraft.
Here are a few other pictures from Mark Stille's book, including closeups of the bridge's final configuration.
A close up of Abukuma's bridge during the Pearl Harbor operation
(sorry it's sideways)
Natori in 1933, with the final bridge configuration
3 different Nagara class ships, from top to bottom
Abukuma during the attack on Pearl Harbor
Isuzu in October 1944 during the Battle of Cape Engano
Nagara in 1944