The hard part about replacing that tubing is fishing it through the block (water jacket). Taking the oil pan off will not help.
A skinny wire like a guitar string can be fished through the old tubing from one side of the block to the other. Now you just need to hold onto the end of the wire as you pull the old tubing out of the block on the opposite side. Then you push the new tubing onto the wire and through block until it comes out on the other side of the block.
