Engine Taking My Cylinder Heads To A Machine Shop.

Complete valve job and replace ALL the valve springs and spring hardware. The 5.0 Mustang HO engine has a roller camshaft that has a very fast opening and closing rate. It requires valve springs that will be compatible with the camshaft's fast open and close. Fail to replace the springs with the Crane or Comp Cams springs and you will have valve float at high RPMs. The valves will play kissy face with the top of the pistons and ruin your whole week. Crane Cams or Completion Cams will have the springs, sping locks and retainers that you will need for the job.

See http://www.compcams.com/Products/CC-'Valve Spring Tech'-0.aspx
OR
http://www.cranecams.com/view.php?s_id=58
and http://www.cranecams.com/userfiles/file/334-343.pdf
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Jrichker nailed it. They will mill the mating surface and clean them up for you. Make sure they add a good spring and new retainers. I think all of that ran me about 250 some 6 years ago, but shop prices will vary. If you have an aftermarket can you are wanting to install give them the specs so they can add the appropriate springs. I think you will be happy with those heads. They aren't going to set the world on fire but if you can swing the whole package for under 400 you will be doing well.