My (unreleased) target window was easy to convert. The size of the v0 page adjusts the size the window is resized to once in game (and using the old style target window), but I didn't calculate the exact relation between v0 size and main window size, I just took screenshots, figured out how many pixels shorter/skinnier I needed and changed the v0 size accordingly.
No screenshot (because this is mainly a posting my-code-sort of post) but here's some ugly ascii art of my window:
Code:
O-------------O
| ^^^ |
|Target's Name|
| =========== |
|Heroic 100%|
| =========== |
|Lvl 0 100%|
O-------------O
Quib