Want to put a magnum 5.9 in my 70 dart.

OP, are you keeping the front serpentine setup, or switching to one of the two different LA timing cover/water pump/pulley setups?
That will determine what you need for a radiator/shroud.
If you're keeping the Magnum's serpentine setup, make sure the 4 bbl. manifold you get has the provisions on it for mounting the serpentine setup, and has the thermostat offset to the driver's side for bracket clearance.