How to Repair the Water Cooling System of a PMG5

One of our French forum members, Aigle4, has decided to repair as well as modify the original water cooling system of his PMG5.
A step-by-step procedure (in French, but with many photos) is available from his personal website: http://nysoyan.free.fr/Eaglefour/PowermacG5.html
Before:

After: