It doesn't. From the 2012 SD Order Guide:

SNOW PLOW PREP PACKAGE (473)
Availability:
• Optional on all 4x4 Pickups
Not available with:
• Heavy Service Front Suspension Package (67H)
Requires:
• 4x4
Includes:
• Computer selected springs for snowplow application.
• Extra Heavy-Duty Alternator (67D) w/Power Stroke® diesel engine
(Heavy-Duty Alternator with gas engine)
Options Available:
• Dual Alternator (67A) (Diesel only)
NOTE: Restrictions apply; see Supplemental Reference or Body
Builders Layout Book for details