Assuming the 318 came from a truck you will need to change the oil pan & pickup (your 360 pan wont fit the 318) The 318 will bolt to your trans, mounts should swap, all 360's are externally balanced so you may have a balancing issue (not sure if late 318's are externally balanced - I know the early ones are internally balanced) you can buy an aftermarket 4bbl manifold to fit the Magnum motor if you want to go carbureted.
im going thru this swap now with an M body.
this is an inaccurate statement.
coupla things,
your 360 car pan and pickup Will bolt right onto the Magnum truck motor and is the one you need to make the swap happen.
your 360 Torque convertor Weight can be removed Very carefully and then you will be able to use your original trans and vertor.
you will Have to use the flywheel/ring from the magnum motor,it is balanced there.
lay the flywheel over the face of your convertor.
one of your holes Will have to be rat filed a hair to make room for that bolt.
now,you can go all the way and install it with efi and the compooter n all that jazzz,or,
you can buy a stealth/attack sb magnum 4bbl intake for around 200 bucks.
same thing goes for the front of the motor,you can keep it stock and serpentine,
or Swap all the La motor/360 front end pieces/timing cover,pulleys etc etc.
if you choose the serpentine belt,be aware you may end up needing to swap the power steering pump from truck to a Van version,the bracket locates differently.
theres a few other details..lmk if you need help or questions.
the Best resource ive found so far for these type of Swaps is the FAbo,or the A body forum.
those guys do these swaps in their sleep practically over there.