Crop+letterbox , same resolution and not (any kind) of resize.. right?

[Selur]

According to what I see, you take a source which is: 720x576, then crop it to 720x576 and then add the cropped off parts back to get 720x588.
I assume this is what you wanted.
To compare it, you can simply co to the Filtering-tab, enable 'Compare view' and look at the Vapoursynth/Avisynth preview.

Cu Selur