Neal, I am responding to your post in the picture series here, due to faster loading time.
There is no practical reason to install new panels over old, since all the rivets have to be removed anyway. Installing pre-formed corner panels over existing would make the installation even more difficult or even impossible, due to thickness of the old panels.
To test your skills with panel replacement, the pre-formed corner panels would be a challenging place to start.
Consider paying someone with experience you could assist in doing the work. It may save you at the bottom line.
The window below the panels would have to be removed and reinstalled in the exact same location. Besides the sealer under the window frame, you may find large amounts of vulkem smeared against the frame from the inside, making removal difficult not having access to the inside of the skin.
Alignment of the new pre-formed panels is critical and difficult. Wedge locks should be used for the first layout.
Masking tape (like 3M blue tape for minimal adhesive transer) should be applied next to the seems, to prevent the vulkem from getting all over the skin.
The curved seams should be riveted starting from the center or else you may not achieve a tight fit.
Below another link to riveting techniques and tools: