Many times I hear of people who have problems with the exhaust gas getting past the crush washer under the injectors on a 6.0 Powerstroke. Most diesel techs that I talk to around the country don't know why there are two styles of injector hold downs or how to tell if they have the correct one.
There are two different styles of injector clamps, one has a rounded back and the other is squared off.
There are two different style of cylinder heads. If you look at the "bump" in the cylinder head that is drilled and tapped to accept the injector bolt, one is drilled dead center and the other is drilled off center.
If the hole is dead center in the bump, the correct clamp is the one that has the rounded back.
If the hole is drilled off center in the bump, the correct clamp is the one that's squared off on the back.
There have been so many head swaps on these things that parts get mixed up. Many times people can get away with using the squared clamps in either head and they don't have a problem right away but a small percentage of the time there's a problem right away with diesel fuel entering the cylinder as soon as the key is turned which can cause a hydro lock situation.
Using the rounded injector clamp in the cylinder head with the off center hole usually leads to the clamp hitting either the rocker box or a valve spring.
If you need a remanufactured engine, buy one from a company who supplies the correct injector hold downs with every reman long block. Asheville Engine, Inc. provides all of the necessary upgrades to give you the best remanufactured Ford Powerstroke engine made.