Do you really have to crop it? Have then print it full size on a 16x20 sheet and trim off the top and bottom areas.
When people want a full-frame shot on 8x10, they either print it
7x 10 or
8x12 to get a full image, and again just trim off or matte over the blank spaces.
Does tend to screw upo using off-the-shelf frames, though.
