"Let me know if you have any thoughts or suggestions. Thanks."
You asked for it:

Keep what you want and throw out the rest.
The nice thing is that Japanese construction standards changed after WW2 to reflect a more American approach. So you can change whatever you want.
First instead of a Mk42 127mm/54, the JMSDF purchased the
Mk16 127mm/54 surplus from the USN and used it quite effectively. The best USN 6" after WW2 was the
Mk16 6"/47 semi-automatic. I suspect that if the JMSDF was willing to give up the DP mission and make it a purely anti-surface weapon they could improve the performance. During the 1950s the
3"/50 Mk27,33,34 was a must as an AAW weapon. (the link over at navweaps can show you pictures of all its many versions with and without a gun house.) The
ASROC "pepper box" launcher came in versions with and without reloads. If your content with 8 rounds and manual reloads you can place it where it fits.
Air search radar:
AN/SPS-6B A pair should do. One on the foremast, and one on the mainmast. For fire control a Mk37 from the ww2 era would sufice for anti surface and AAW you can replace the mk12 and mk29 radars on top of the
Mk37 with the mk25 dish radar.