There are a few crop choices on 1Ds MK3, it then became cropped in the raw file, and I don't usually do it. …
Just to make things clear (from the 1Ds Mk3, page 178), I added the bold emphasis:
During Live View shooting, vertical lines corresponding to the aspect ratio will
be displayed. You can thereby simulate framing for medium- and large-format
film sizes such as 6x6 cm, 6x4.5 cm, and 4x5 in. This aspect ratio information
will be appended automatically to the captured image.
(The image will not
actually be saved to the memory card as a cropped image.) When the image is
transferred to a personal computer and the Digital Photo Professional (provided
software) is used, the image will be displayed in the aspect ratio you specified.
0: Off 4: Aspect ratio 6:7
1: Aspect ratio 6:6 5: Aspect ratio 10:12
2: Aspect ratio 3:4 6: Aspect ratio 5:7
3: Aspect ratio 4:5