For basic approval on the KS armor, not much. And this goes for any armor currently available. You'll need to add the grey rectangle on the front chest part (usually paint or decal), add a cloth cover to the chest/back join, paint the tank topper with a white circle and a red line, and remove the extra clear tubing that KS will include on the armor edges. After that, you could be approved in it provided the fit is good for your body type.
For better look-and-feel and more accuracy: replace and/or reshape the shoulder bells, replace the belt boxes (way too large), replace the nylon webbing with real cotton webbing, replace the greeblies (t-bit, snout, and add TD bits), replace the TD end caps, replace the helmet bolt covers, replace the snout, and replace the helmet decals. I'd also replace all the Velcro/Elastic strapping since KS uses a cheaper brand. You could also go screen-accurate on the strapping.