I have to purchase head gasket and head bolts for my 2006 f250 6.0 (imagine that) and need my serial number off from my engine to figure out my head gaskets. They offer 2 different post sizes 18mm or 20 mm. Trying to have my parts in line before tearing it down.

 

You will find your engine date of manufacture and serial number on a label on the FICM module. You will also find the serial number stamped on the left rear corner of the block.

Page 8 of the 6 liter Powerstroke Bible.