Steel plugs in aluminum heads & their inherient issues have been around since the 70's- unless you are talking racing products from the 60's (which I'm not)

When I decided it was time to change the plugs (2006 Mark LT 4x2, 5.4, 35,000 miles) I used the Motorcraft SP 515’s. Although I knew about the carbon build-up/plug removal issue, I decided not to change the plugs until there was a replacement plug that I was comfortable with…meaning I knew it was a good quality plug in terms of component design and construction. Although I did following the most recent TSB, I also relied on my experience back in the 1970’s when aluminum heads & intake manifolds were just entering the street scene and never-seize did not exist. Here are the exceptions to the TSB that I did…
1. I ran Lucas fuel injection cleaner, mixed at 3 times their recommendation in 1 full tank of gasoline. Purpose…if I was lucky, it would dissolve or loosen any carbon buildup (although many do a real fuel injection cleaning also- and it is probably a best practice to do if you have more than 45-50,000 miles on the plugs)
2. Although I am a fan of PB Blaster, I used a product called ChemSearch “Yield”. The issue I have with using carb cleaner is the lack of lubrication…..in the old days of removing steel plugs from aluminum heads, we use to mix up acetone & ATF…or of we needed more lubrication, kerosene & ATF, “Yield” provides this lubrication- much better IMHO than even PB Blaster.
3. Yes, I put anti-seize on the plug threads (I know the TSB says not to)
4. Of course…a lot of patience, I really doubt if I ever put more than 20-25 lbs of force during removal (purposefully)
The end result, only one plug even “squeaked” coming out (but it basically unscrewed like a regular plug- literally). Plug #4 was initially a little stubborn, but after the second try, then waiting about 30 minutes, it came out with very little effort…just kept wiggling the plugs (tightening/loosening) by 1/8th or even less of a turn- and they all came out without a single one breaking or any issue really.
Actual working time: 2 hours…..including washing my hands, total time was 5 hours.
FYI- Why I choose Motorcraft.
In the 1970’s I ran (like many) Champion’s in just about everything (even had the gold palladiums), but stopped in the early 1980’s when they changed their copper-core design and the resulting quality problems that IMHO still exist today. Since then I have run Splitfire (non-platinum) in my old world (1960’s) cars, Bosch in my late 1990’s vehicles (both because the cylinder head design really prefers these types of plugs), but I really had hesitation because of the construction/component quality of the non-Motorcraft plugs and really questioned the durability in this application about the Motorcraft SP508 or SP 509’s which are single platinum. Given the types of loads and burn/flame promulgation rates in the chambers, I really had doubts about the style of the plug with single platinum having the ability to “survive” as long as they engineers said. What do ya know…the SP 515’s are double platinum.