Maxwell Camera Offset
Update 1.1: Added exposre dialog for adjusting parameters without changing camera exposure, and support for render regions in the offset viewport.
I have a new script that displays the Maxwell camera offset in the viewport. You can switch it on and see a masked region of the viewport (make sure safe frames are turned on) and move the camera, pan, zoom, etc. with it on.
If you have any problems or bugs or suggestions for improvements, let me know!
Run the .mzp file and then restart Max. You will then have a dockable / floatable toolbar with the controls.