Pair GM Chevrolet 5.0L 305 Mercruiser Cylinder Heads – Casting Numbers 059 and 520 | 12552520 12558059 W/ Head Gasket Set and Bolts

Enhance your engine’s performance with the GM 5.0L 305 Cylinder Heads, featuring Casting Numbers #059 and #520. This complete set includes fully assembled cylinder heads, a head gasket set, and bolts, designed to meet or exceed OEM specifications for a perfect fit and reliable performance in marine environments. Built to withstand high heat and moisture, it ensures a quick, hassle-free installation for your GM 5.0L 305 engine.

Key Features:

• Compatible with GM Chevrolet 5.0L 305 and Mercruiser marine engines
• Casting numbers #059 and #520 for OEM fit and performance
• Includes head gasket set and bolts for easy installation
• Fully assembled with valves and springs for hassle-free setup
• Designed for marine applications, offering exceptional heat resistance and durability
• Perfect for engine rebuilds, repairs, or performance upgrades

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 – Quality You Can Trust

At Heavy Duty Parts Company, we take quality seriously. We thoroughly clean, inspect, and pressure test each cylinder head to ensure it meets the highest standards. Our state-of-the-art equipment is used for all seat and guide work, resurfacing, and vacuum testing. Whether you’re replacing a worn cylinder head or upgrading for enhanced performance, our cylinder heads exceed OEM standards, ensuring reliability and efficiency.

Warranty Information:

• Coverage: Heavy Duty Parts Company provides a two-year unlimited mileage parts warranty. A warranty card will be included with your invoice.
• Terms: By purchasing the cylinder head, you agree to the following warranty terms:
  • Keep the heat tab intact and unaltered.
  • Include a copy of the invoice and a Return Authorization number for returns.
  • The warranty covers parts only; labor and incidental costs are not covered.
  • The warranty does not cover damage caused by improper installation, overheating, abuse, or neglect.

Order Your New GM 5.0L 305 Cylinder Heads Now!

Ready to upgrade your vehicle? Order your premium New GM 5.0L 305 Cylinder Heads today and experience enhanced performance and reliability.

For questions or assistance, please contact our customer service team by email at sales@heavydutypartscompany.com.

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!

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