The F250/F350 srw currently are basically all the same components and have been for a long time. What you get different:
2 vs 4" lift block on the rear end 250/350
Different rate spring packs/coils depending on option codes, in some cases the diesel gets close to the max spring rate and there aren't any ++ options.
5.4 L has only 2 sidegears in the same 10.5" rear axle as it is putting less torque through diff. (this isn't always true, some 5.4's got the v-10/diesel carrier +side gears)
F250 has lighter+smaller tires and in some cases lighter duty rim options - but not always.
Bellhousing casting on transmission different.
Torque convertor specs different (obviously)
They have the same transmissions, transfer cases, driveshafts, wheel bearings, ring and pinions, axle shafts, brakes, rear springs, frames, etc regardless of engine. Frame psi/thickness based on the wheel base.