Any way to make a custom grid/page size?

I realise this is a very basic question for this forum, so I apologise in advance.

The course I teach on has used CorelDraw for 2D drawing and Rhino for 3D drawing for as long as I can remember. They are finally switching this over to everything on Rhino, but it means documentation needs updating.

When using CorelDraw to link with the laser cutters we have students set up a Template document with a page size of 600mm wide, by 400mm in height, the maximum cut size of the laser cutter.

I know the grid size can be changed, but the best I can do is 600mm by 600mm, I’m guessing the grid will always be square?

Are there any alternate ways of creating a Rhino Template document that has a restricted some form of on screen indication of a 600mm by 400mm draw zone?

Thanks

Just have a rectangle on a layer that’s part of the template?