Subfixer's right. It builds into nice kit out of the box.
However, if you just have to spend some money or want it 'uber' realistic, there's several options.
L'Arsenal produces several components (5" turret, Bofor gun mounts,etc) that enhance the kit.
Here's a link to thier 1/350 offerings
http://www.larsenal.com/GB/catalogue/Arsenal/1_350.php
You can get their products direct from their site or from White Ensign Models and Pacific Front Hobbies' websites. They'llalso have other vendor listings for 1/350 Fletcher parts.
But to put things in perspective, I just purchases a Trumpeter 1/350 The Sullivans Fletcher class destroyer kit. L'Arsenal has a comprehensive upgrade kit to do everything - turrets, 20MM & 40MM gunmounts, radar sets, etc. Now my kit from Hobbytown USA cost $30.00. The upgrade set is going for $60.00.
I don't do this for every kit but I have a select few I like to be more lavish about.