As they said before you need a thick metal plate with a hook on it. This is slipped in the bracket at the rear body that has the rusted screw in there. On this you fix the lid hinge again with a little hex nut. In the hook will the rear bar be attached. See the hooks righthand side in the bottom circle

Yes, the parcel shelf straight bar does fit into the same hook-plates as the hatchback kit in the AZL57's picture, but don't be confused by everything else in that picture, (that you don't have or need, for fitting a parcel shelf).
The rusty headed screw in your photo needs to come out. It probably goes into a captive cage-nut: remove that as well. Then slide your new hook-plate down behind where you removed the cage-nut from and hold it in place with the M5x0.8 screw (8mm hex head), through into the threaded hole in the hook-plate.
The curved bar it attached to the back of the seat, (with the self-tapping screws), through the seat material, into holes that are often already pressed into the frame, (but they are quite hard to feel through the material).

My 2CV has the "half hatch" unlike the model shown above. Maybe folding the rear seat forward will help me determine how to mount the curved bar in the seat back.

You would think as many how to do videos Burton has installing one of these would be one of them!

This weekend being Christmas, I probably won't have any time to look at it until next week when I am off.

By the way, Merry Christmas! Hope Santa brings you everything you wanted for your 2CV!

We did only speak about the hooks that you need, the rest of the fittings is of no use to you...

Well the hooks, two bolts, two tapered head screws and the two bars are all that came with the kit. I didn't get any of those other parts.

Than you have all parts needed. Best to take the rear seat out, that is easier to fix the curved tube to the seatframe and sitting in the boot without the seat is easier to install the hooks.

This morning before shoving off for work I grabbed one of the hooks and I now see how it fits. The curved bar still doesn't seem to make sense at the moment. It looks like it's supposed to go underneath the top curved portion of the seat bar (under the vinyl covering) but doesn't quite match up with the contour.

Maybe once I pull the seat it will make more sense.

I'll check it out next week when I am off.

It goes on top of the vinyl. You have to locate the pre-punched holes in the top tube of the frame and poke the screws through the vinyl. On ours there is also a hook pop riveted to the middle of the seat tube which locates in a hole in the parcel shelf tube.