rockauto.com only shows the DG508 as fitting a 2005. I guess they could be wrong.
Have you visually confirmed it?
Buyer's Guide: MOTORCRAFT DG511 Ignition Coil
FORD EXPLORER (2006 - 2008)
FORD EXPLORER SPORT TRAC (2007 - 2008)
FORD F-150 (2004 - 2008)
FORD F-250 SUPER DUTY (2005 - 2008)
FORD F-350 SUPER DUTY (2005 - 2008)
FORD F-450 SUPER DUTY (2005 - 2008)
FORD F-550 SUPER DUTY (2005 - 2008)
FORD MUSTANG (2005 - 2008)
LINCOLN MARK LT (2006 - 2008)
LINCOLN NAVIGATOR (2005 - 2008)
MERCURY MOUNTAINEER (2006 - 2008)
Buyer's Guide: MOTORCRAFT DG508 Ignition Coil
FORD CROWN VICTORIA (1998 - 2011)
FORD E-150 (1997 - 2014)
FORD E-250 (1997 - 2014)
FORD E-350 (1997 - 2014)
FORD E-450 (2000 - 2014)
FORD E-550 2002
FORD ECONOLINE SUPER DUTY (1997 - 1999)
FORD EXCURSION (2000 - 2005)
FORD EXPEDITION (1997 - 2008)
FORD EXPLORER (2002 - 2010)
FORD F-150 (1997 - 2010)
FORD F-150 HERITAGE 2004
FORD F-250 (1997 - 1999)
FORD F-250 SUPER DUTY (1999 - 2004)
FORD F-350 SUPER DUTY (1999 - 2004)
FORD F-450 SUPER DUTY (1999 - 2004)
FORD F-550 SUPER DUTY (1999 - 2004)
FORD MUSTANG (1999 - 2004)
LINCOLN NAVIGATOR (1998 - 1999)
LINCOLN TOWN CAR (1998 - 2011)
MERCURY GRAND MARQUIS (1998 - 2011)
MERCURY MOUNTAINEER (2002 - 2010)