5.4 PI motors from the heads down are essentially the same with the following exceptions.
All lightnings came with forged crankshafts. Expy's came with cast cranks but I understand at some point they installed forged cranks they had on hand so could not tell you which may or may not have them.
Lightnings had forged lower compression pistons. Expy have higher compression hypereutectic pistons. Forged pistons are far more forgiving but you can run tighter tolerances with the hyper pistons. So typically you only see forged pistons in boosted applications.
Lightnings come with a 6 bolt torque converter thus the flex plate has 6 holes to match. Expy's have 4 bolt converters.
I understand there may be slight differences in the timing cover but not sure what they may be. I had no problem mounting all the lighting hardware on mine.
The 5.4 motors weak link are the powdered metal connecting rods. Beyond 450 ish rwhp (this is well over 500hp at the crank) they have been known to exit the block. Connecting rods should be the first thing you address if you plan to make serious power and or rebuild the block with boost in mind.
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