Duramax Billet Flex Plates SoCal Diesel’s billet flexplates are lighter and stronger than stock. They meet the new SFI 29.3 specification for competition use. 3 separate part numbers are properly counterweighted to install on an already assembled engine without the need for re-balance. · 2001-2005 LB7/LLY Engines. · 2006-2010 LBZ/LMM Engines. · SoCal Diesel Stroker Engines.