So, err, that didn't work. I guess I didn't account for a two big things:

1. The difficulty of removing support material near thin walls
2. The fact that the printer doesn't print lines with 0 width
   

(1) caused the slots where the ground tap inserts in the back of the shell to be impossible to clean out without destroying the walls that would hold the tab in place. 

(2) caused the hole for the DC plug to be just about exactly the size of the plug itself rather than 1mm larger, so, um, it didn't quite fit...

This was cheap enough that I can try and fail a fair number more times before I would have been better off just replacing the part online, so I will revise my design and upload it once I am ready to try another print.