GM Chevrolet 5.0L 305 Mercruiser Cylinder Head – Casting Numbers 059 and 520 | 12552520 12558059

Introducing the GM Chevrolet 5.0L 305 Mercruiser Cylinder Head – Casting Numbers #059 and #520, specifically designed to restore and optimize the performance of your 5.0L GM Chevrolet or Mercruiser marine engine. These high-quality cylinder heads are built to meet or exceed OEM specifications, ensuring a perfect fit and reliable performance in your marine applications.

Crafted with precision engineering, these heads feature the #059 and #520 casting numbers, making them the ideal replacement for worn or damaged components in your GM Chevrolet 5.0L engine. Whether you’re upgrading for improved reliability or conducting an engine rebuild, these cylinder heads offer the durability and performance necessary for demanding marine environments.

Built from high-strength materials, these heads are designed to withstand the extreme conditions that marine engines face, including high heat and constant exposure to moisture. Fully assembled with valves and springs, they allow for quick and easy installation, minimizing downtime and getting your boat back on the water faster.

Key Features:

• Compatible with GM Chevrolet 5.0L 305 and Mercruiser marine engines
• Casting numbers #059 and #520 for OEM fit and performance
• Fully loaded with valves and springs for hassle-free installation
• Designed for marine applications, offering excellent heat resistance and durability
• Ideal for engine rebuilds, repairs, or upgrades
• Core Return Required

Applications:

• Fits GM Chevrolet 5.0L 305 and Mercruiser marine engines
• CHEVROLET 1500 PICKUP 96-99 8-305 (5.0L);
  CHEVROLET 2500 PICKUP 96-98 8-305 (5.0L);
  EXPRESS 1500 VAN 96-02 8-305 (5.0L);
  EXPRESS 2500 VAN 96-02 8-305 (5.0L);
  GMC 1500 PICKUP 96-99 8-305 (5.0L);
  GMC 2500 PICKUP 96-98 8-305 (5.0L);
  SAVANA 1500 VAN 96-02 8-305 (5.0L);
  SAVANA 2500 VAN 96-02 8-305 (5.0L);

Whether you’re performing routine maintenance, engine rebuilds, or simply looking to restore your boat’s performance, these cylinder heads offer reliable power and long-lasting durability. Designed to handle the harsh conditions of marine environments, they ensure your engine performs at its best, no matter where your adventures take you.

Heavy Duty Parts Company – Core Returns Policy

Effective December 17, 2025

At Heavy Duty Parts Company, core returns are essential to our ability to provide high-quality, cost-effective cylinder heads. Returned cores supply critical components—such as keepers, springs, and retainers—that are vital to proper engine performance and allow us to maintain OEM-level quality.

No Upfront Core Charge

Unlike many suppliers, we do not charge a core fee upfront. Instead, we rely on customers to return their used cores within the required timeframe.

Core Return Requirements

• Cores are due within 30 days of the purchase date

• If a core is not returned within 60 days, the product warranty is void

• Unreturned cores will be charged as follows:

  • Cylinder heads under $600: $200 per unreturned core

  • Cylinder heads $600 and above: $400 per unreturned core

Customers needing additional time may contact us to request an extension. Approved extensions will prevent core charges from being applied.

Core Return Process

Cylinder heads are shipped with prepaid core return labels included in packets attached to the outside of each box. If labels are missing, customers should contact us for replacements prior to returning the core.

Core Eligibility

Some cylinder heads do not require a core return. In certain cases, core requirements may be waived at our discretion.

Why Core Returns Matter

• Reused core components help maintain OEM-quality standards

• Core returns allow us to keep pricing competitive

• Recycling cores supports sustainability by reducing waste and conserving resources

This policy applies to all purchases made on or after December 17, 2025.

Send Back All Components

To ensure the quality and integrity of our remanufacturing process, we ask that you return all components that were originally included with your new cylinder head. This includes items such as:

• Rocker arms
• Camshafts (if applicable)
• Any other hardware that came with your purchase

Easy & Free Core Return Process

• Each purchase includes a prepaid core return label in a plastic sleeve on the box.
• Simply pack your core with all included components, attach the label, and drop it off with the carrier—no extra cost to you.
• Returned cores undergo inspection and recycling, ensuring maximum efficiency.

Customer Partnership & Sustainability

By returning your core and its components, you help maintain a reliable supply chain, ensuring we can continue offering top-quality products at the best prices. This process not only benefits your wallet but also contributes to a greener and more efficient automotive industry.

We appreciate your support in keeping our business and the industry running smoothly!

Shop

Mercruiser