Roger that.
The Duratec, much like the Mazda KL Series motor is internally balanced, and will not perform worth anything if not properly balanced after the install of any afternarket internal parts, such as pistons, rods, etc.
Most machine shops will be able to re-balance your rotating assembly, and those who have their blocks rebuilt by a machine shop should already know to do this, but reminding them wouldn't be such a bad idea.
--Adam
