It should fit, but will need a LOT of work. Having the entire donor vehicle helps. You'll have to change the entire fuel system (should be able to keep tank, but will need some mods) and the electronic system. Swapping computers may be a challenge -- most now sense a module in the instrument cluster so if you pull the computer you can't use it in another vehicle. You might have to use an aftermarket computer or get the factory ECU reprogrammed... unless you can swap the instrument clusters as well. You will definitely need to upgrade the front springs for the heavier engine, and maybe other suspension components. F-250s still use a Twin I-Beam front suspension, IIRC, not the double wishbone of the F-150/Expy.