Well the exhaust flow is, 2 exhaust manifolds- 2 up pipes-Y pipe-turbo-tail pipe. One of the "up pipes" vents to the cooler, then to the egr valve, then intake.
If you only block the valve, the exhaust will swim arround the cooler, sill puting in heat. if you block the the cooler then the entire system is saved from the exhaust.
Some later models have a scoop on the up pipe that forces exh into the egr system. It covers half the pipe. Its a good idea to cut that.
It is easy and cheep to cut out a metal plate in a circle and weld it on for less than the valve block or sneeky pipe. If you dont have the suplies then get a friend.
^^^^ this is if you dont buy the sneeky pipe.
Its good to get the valve block, but if you are going to decide on only one modificatoin then^^ this is better. If you dont want to do any of the above then get the valve. Some thing is better than nothing.
Here is another option.
Since the egr system and intake are connected, the egr valve block will hold the intake pressure in the intake and the welded cooler will keep the exhaust where it should be. That would be a great set up.
Here is a picture of the scoop at the bottom of the page.
6.0L EGR Components
These 2 links show the flow.
6.0L Bible Table of Contents
Powerstroke 6.0L Technical Intro Manual