I'd have to look it up to be sure, but if I remember correctly there were in fact three bridge configurations among the class during the war. The Iowa was commissioned with an almost completely open bridge. The New Jersey's was enclosed, but rounded on the front. The Missouri and Wisconsin had the squared-off, enclosed bridge structures that we usually associate with the class.
All four eventually got modified, and wound up with extremely similar bridges. I'm not sure when that happened in each case. I'm pretty sure the Iowa got her new bridge before the war ended; it sticks in my mind that the New Jersey may have retained the enclosed, rounded configuration until sometime after the war. I think all this is covered in Robert Sumrall's book, Iowa-Class Battleships.
They also differed, of course, in numerous details - anti-aircraft gun layouts, aircraft, etc. And the Iowa had (and, I believe, still has) a special bathtub somewhere in her superstructure to accommodate FDR during his trip to the Casablanca Conference.
I believe the only kits that acknowledge the different bridge configurations are the excellent Tamiya 1/700 ones. The Tamiya 1/700 Iowa has the open bridge and the Missouri has the squared-off, enclosed one. I'm trying to remember the old 1/700 Fujimi kits; I think the Fujimi New Jersey just may have had the rounded bridge, but I'm not sure.
Hope that helps a little. Good luck.
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