Shore power receptacle

As some will know from my other posts, I'm in the process of adding a hard-wired EMS to my new T@B 320. There are limited options for mounting the unit and all of them require adding wire to the run from the shore power receptacle to the WFCO. I thought I'd just remove the existing connection to the shore power plug, and add a new wire to the EMS unit from there, but I can't see how the plug and receptacle can be separated. Hoping some who may have done something similar can help.

It looks like the grey tab locks the wire to the retaining box, which in turn looks like it's held to the back of the receptacle with some press-in tabs. Nothing separates easily however, and I don't want to force anything, There is a set screw (visible just under the tab, at the bottom of the receptacle) that I loosened but it too did not seem to free anything up.

I also checked to see if backing off the retaining screws from plug would help. Again, nothing comes apart easily.

Appreciate any advice.