From looking at and measuring the frames they appear to be the same but with obvious differences like the cross members, spring hangers, engine mounts. I know the f250 uses 3 inch wide leaf springs in the back whereas the f150 leaf springs are 2 1/2 inches wide.
For the front suspension I am contemplating trying to remove the cross member from the f250 diesel and putting it in the f150. Has anyone done this? if so what kind of problems can I expect?