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Distance between the frame rails would be the same---because the bodies will fit on different GWV chassis that distance is critical.
The E250/350 are a bit taller in section height and web thickness. E450/550's are taller and thicker than the E250350's.
All are equal distances apart. Consult a Ford Body Builders manual for exact dimensions. Once upon a time they could be readily found and downloaded online--not sure if they're still available.