the Magnum still has the same ears on the block as the LA engines do(though they don't use them anymore in trucks other than maybe a B van, they are there) with the right oilpan it should bolt right in!
On that oilpan; when they went to the Magnum they changed the 318 to accept the same style oilpan as the 360; LA OR Magnum. so get a 360 pan and pickup and you should be good.
Had to do the same to put a magnum into my Volare.