Swapping a 360 from A-Body/auto into a '78 Dodge Van with factory 318/4 speed - Advice?

You should be able to modify the 318 engine brackets to fit the 360

You will likely have to buy a 360 flywheel

In the mid 70's I had a 360 in an old Landcruiser, later a 340. I had a balanced flywheel (340) and knew better, but ran it anyway. IT DID SHAKE at some RPM points.