But anyways, here's a Fuse that draws a letterbox overlay as a viewshader, which means there's no longer any need to drag around a resize or letterbox node in your flow to check how the final result will be framed. The difference to Fusion's guides overlay is the fact that this fuse works with any image size. You can define any custom aspect or even the width of the top and bottom bar independently in pixels. I once had a project with a 1.85 frame format that was off-center inside a 3K film scan.
you can find it on vfxpedia. Enjoy :-)