as the spruance class update program originally included this system, as did the CSGN program, and the gun was tested and worked. it would be weird if it didn't, because it was based on the long history of cruiser guns. the concept wasn't flawed, but the USN apparantly didn't see the need for it, and thus it was never installed. not an reason to not install it here to me
that said, back to the design.
I see no reason to lengthen the ship again.
the only way to enlarge the powerplant would be adding diesels, adding gas turbines or making the entire thing nuclear.
compare your ship with the CSGN's and try to find a ship with the same weaponnery. you will, I think, find out that your ship is larger then those CSGN's, while it should be smaller due to the more compact powerplant. (look at DXG and DXGN, the kidd and the virginia classes)
so, the question is what has gone wrong here.
the only reason why it would be bigger then an virginia would be the command spaces. so it would end up close to what you had earlier on this page..... I see no need to enlarge it further. (also, I think you have again blocked the plenum vents to the Mk 26, or are the ABL's at the beam entirely?