WOW... you had the same crappy bit of aluminium... lol
Before I put the plastic back on I took a file to the sharp bit at the top which was making a right mess of the plastic. I also noticed that the bottom is not cut straight, so I filed back that as well.
Then (you can see in the second photo I posted the post is not tall enough as the plastic sits above the metal strips behind the three targets. Its about 4 or 5mm too short. So I has some of that thick self adhesive felt backing used a protectors on the bottom of ornaments and such like so I made a spacer to go on the bottom of the post.
Yes it look like the white post is a added extra as your plastic only has two holes whilst mine has three. Perhaps in the field this plastic part was breaking all the time so the tech decided to secure it better with a third fastening point.