45 Degree Guidelines

I'm setting up a modular grid and I want to change it into guides, but I want to set guides at 45 degrees as well as horizontal and vertical guides.

I know that the lines I have drawn (Magenta and Cyan) can be converted to guides, but ideally, I would like the guides at the 45-degree angles not to extend past the top, bottom, right and left-hand edges of the rectangle.

Is there a way a fast way of doing this?

I have attached 4 screenshots any help appreciated.

Thanks.