12000-ZVT-406ZA Block Assembly *NH8* - Overview. The 12000-ZVT-406ZA Block Assembly *NH8* is a critical component supporting the cylinder system within Honda marine engine systems. This part plays a vital role in maintaining the structural integrity of the engine's block, ensuring reliable operation and longevity. Designed to seamlessly integrate with existing marine engine hardware, the assembly helps sustain optimal engine performance and durability under demanding marine conditions.. Key Feat