GM Chevrolet LS Gen III LM4 5.3 5.3L OEM Aluminum Bare Engine Block 12566910Condition: NEW NEW TAKE OFF The GM 12566910 5. 3L 325 cid Engine Block is a Gen III aluminum block used in Chevy and GM vehicles between 2003 and 2005. This lightweight aluminum block referred to as the LM4 features cross bolted mains and was originally designed for models like the 2004 Chevy SSR Trailblazer EXT GMC Envoy XL and Buick Rainier. Engineered for performance and durability the LM4 block provides an excellent foundation for high performance