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I have a STP (S9549) and the instructions for the adapter all reference a 6.0. So you are probably right about going with a motorcraft.
How about the spring compression? The new filter looks physically identical to the old filter, but I can't seem to get it seated enough to engage the cap's threads.
Really, I would not use the STP filter.
Get a Motorcraft or Fram and snap it in the lid, then install it, should not take excessive force to get threads engaged.
Tip:
I almost messed up a couple times as the top of the old filter would remain in the covering canister. Then you have to place excessive pressure to retighten the canister. Best advice: Make sure the element being removed is identical to the new element and use motorcraft or fram. The oil filter for the 6.0 and 6.4 are identical.
I've been using Donaldson filters on both my 6.0 and my 6.4. The 6.0 has well over 200,000 miles with no problems. I use them for oil, fuel and air. They do not have a fuel filter for the 6.4 yet. Fuel filters are not the same.