A few, perhaps. You will need the flywheel from a 5.2 Magnum as they are different in the crank register area. You will need the oil pan from the 273......and I think it will fit. Maybe another more Magnum knowledgeable will confirm that. If you plan on staying carbureted, you will need an intake manifold for the 5.2 as they are different in the intake manifold retaining bolt area. The early engine has a different intake bolt angle than the later. Of course you will need to figure out what to do for accessory brackets. I would try to get everything from the Magnum and go serpentine. That will require an A/C delete pulley unless you plan on using the compressor with the Magnum. I believe the motor mounts are the same.....but I'm not certain. Something stands out in my mind about a possible difference there.......none of the differences however are deal breakers and are easily worked around. Many people have done the swap.
