Blizzard, it isn't a spark plug issue, it is a quality control issue and it has been for many engines from 1994 (according to my ford contact) to 2008.
The seriousness of this issue seems to be on par with the dreaded dowel pin issue with the millions of Cummins engines and the NTSB and the FTC should have treated both of these the same way they they have treated Toyota's mess.
It seems to apply to the Modular engine aka triton with aluminum heads.
Oh as for the Mustang mess, their QC has been crap for a long time, their unnamed SV supplier rejected two truckloads of heads that were porous that there were 1cm gaps in the casting - no one knows how many are on cars other than Mustangs.
But here is the entire TSB;
TSB # 07-21-2
4.6L 2V, 5.4L 2V, OR 6.8L 2V - SPARK PLUG THREAD REPAIR PROCEDURE - NOT COVERED UNDER NEW VEHICLE LIMITED WARRANTY
Publication Date: October 17, 2007
FORD: 1997 Thunderbird
1997-2004 Mustang
1997-2008 Crown Victoria
1997-1999 F-250 Light Duty
1997-2004 Expedition
1997-2008 E-Series, F-150
1998-2004 F-53 Motorhome Chassis, F-Super Duty
2001-2005 Excursion
2002-2006 Explorer
LINCOLN: 1997-2007 Town Car
1998-1999 Navigator
MERCURY: 1997 Cougar
1997-2008 Grand Marquis
2002-2006 Mountaineer
This article supersedes TSB 07-15-2 to update the vehicle model years.
ISSUE:
Some 1997-2008 vehicles equipped with a 4.6L 2V, 5.4L 2V, or 6.8L 2V engine and aluminum cylinder heads may experience a spark plug port with stripped or missing threads.
ACTION:
Follow the Service Procedure steps to correct the condition for non warrantable repairs.
SERVICE PROCEDURE
Ford Motor Company now authorizes LOCK-N-STITCH aluminum insert and tool kit as a proper repair procedure.
Follow the procedure included in the tool kit for using the tools and inserts. Tool kits and inserts can be ordered from Rotunda by calling 1-800-Rotunda (768-8632). Choose option two (2), part number 302-00001.
NOTE: FORD MOTOR COMPANY HAS DETERMINED THAT REPAIRS MADE WITH THESE ALUMINUM INSERTS AND LOCK-N-STITCH TOOLS DO NOT AFFECT THE HEAT TRANSFER FUNCTION BETWEEN THE SPARK PLUG AND THE CYLINDER HEAD.
NOTE: THIS PROCEDURE IS NOT AUTHORIZED AS A FORD WARRANTY REPAIR. FOR VEHICLES WITHIN WARRANTY, REPLACEMENT OF THE CYLINDER HEAD IS RECOMMENDED.
NOTE: THIS IS THE ONLY FORD AUTHORIZED PROCEDURE FOR SPARK PLUG THREAD REPAIRS.
NOTE: THIS PROCEDURE IS AUTHORIZED FOR ESP REPAIRS AND RETAIL REPAIRS.
WARRANTY STATUS:
Information Only - Not Warrantable