Looking at the pictures, the front turret would be a bit in front of the first AA position on the Chitose deck, the 2nd AA and its little "overhang" mount goes away, and most of that "blob" with the smaller AA above that (20mm??) gets cut back, and the main deck house then is cut back a bit, making room for the 2nd main deck gun turret, with a 3rd one then on the 2nd level... correct?... stack has to get moved back (what'd they do, side exhaust??), maybe some slight changes to the hanger deck area, and you've about got it... but don't forget the mini-subs on deck, along with the sea planes!...
Just a little background on the ship:
http://www.combinedfleet.com/Nisshin.htm
http://www.combinedfleet.com/atully10.htm
http://www.combinedfleet.com/cvlist.htm
why they put the Seaplane Tenders in with the carriers, I dunno, but... note that the Mizuho is also similar, though with a hangerdeck area that is quite a bit different in the few pictures you can find of it. All three of them appear to be different ships in all of their photos, and gun changes appear to happen every time they docked... The Akitsushima appears to be quite a bit different from the others, but who knows??...
Now, come on Faith, you got further with your edits than I ever did... you can do this! But, maybe we really should call on Zuikaku or noshiro?...
