How'* the truck running now still ok without trouble? Get the other 5 done.
The PZH-14F is still a Motorcraft Spark plug was it redesigned to not fall apart ?
Many sites recommend anything but the Motorcraft.
ID be writing a Thank You Ford Letter, for your wonderful customer service, & excellent spark plug, concept design!
It'* moments like this where the guitar comes out to play, two songs come to mind...
"Take the Money & Run" & re the spark plug.."Stuck In the Middle"..with you!

Maaaaaybe if empty and driven nicely at low RPMs, but the 5.4 isn't known for low RPMs . . .

. . . but no way when loaded and going over the rockies unless the damage is waaaaay less than we all think it is.

Yeah, most of the landscape and roofing Ford SD trucks around my way are either F250 or F350 5.4s, an we had them issued by GSA when I worked for the USAF. F250s were short bed crewcab 5.4s and F350s were long bed crewcab 5.4s . They did okay but you could definitely tell it was a little engine pushing a big box. All of the 1999+ Ford Super Duties I've seen in the junkyards that weren't totaled in a wreck are 5.4s. I feel bad for the engines in that combo.

Yeah but then he'd have to buy an adapter plate to blow up his transmission.

The truck is at the dealer, getting the other five plugs replaced, and asked the dealer to re-scope cylinder #4 for a second opinion.

Found a local guy with a 5.4 he said was pulled from a 2005 F250 with 110k miles. Went to look at the engine, but the truck it came out of is not there, no way to verify the actual mileage of the engine with no vin, let alone know if the engine was running properly when pulled. He was asking 1200 for the used engine, then said he paid 800 and would not take less.

Seems not a bad price for what he says it is. I don't think much changed between 2005 and 2007 model years on the 5.4, but a true Ford guy might be able to tell you more. Some states won't allow an older engine, even otherwise exactly the same, to replace an engine in a vehicle, although they seldom actually inspect for date codes etc.

An idea: See if you can get the VIN of the donor truck, CarFax it, and see if that history jives with the mileage the seller is claiming.

Quick update, brought truck to the local Ford dealer to have the five remaining original plugs replaced, and to rescope cylinder #4. Dealer stated five plugs replaced without issue, scope of #4 showed some surface damage to piston, but cylinder wall showed no damage. Stated compression a bit low but not unusual for a truck with 90k miles. They ended it by implying the truck is fine to drive.

I like your wording. They don't want to guarantee anything (and I don't fault them for that) while at the same time telling you it'* probably okay enough. Did they happen to give you a picture of the surface damage?