Numbers Matching

Numbers matching means the car retains its original, factory-installed engine, transmission, and sometimes rear axle—verified by stamped or cast serial numbers that correspond to the car's VIN and factory documentation.

On classic Mustangs, this is verified through:

Engine block casting numbers - Stamped on the block (usually on the passenger side, near the bellhousing). These indicate:

• Engine displacement (289, 302, 351, etc.)
• Build date
• Assembly plant
• In rare cases, partial VIN matching

Transmission serial numbers - Stamped on the case, indicating:

• Transmission type (C4, C6, Toploader, etc.)
• Build date
• Assembly plant

Rear axle date codes - Stamped on the housing, showing:

• Gear ratio
• Build date
• Assembly plant

For a Mustang to be truly "numbers matching," these components' build dates must be consistent with the car's scheduled production date (usually within weeks or months), and in some high-value cars (Shelbys, Boss models), the engine block has a partial VIN match.

Here's the reality: most classic Mustangs are NOT numbers matching. Engines get rebuilt with replacement blocks. Transmissions fail and get swapped. Rear axles are upgraded. After 50+ years, original drivetrains are rare.

Numbers matching matters most on:

• Shelby Mustangs (GT350, GT500, etc.)
• Boss Mustangs (Boss 302, Boss 429)
• High-option factory cars (Mach 1 428 CJ, GT390, etc.)
• Competition or special-order builds

On a standard 289 coupe? Numbers matching adds modest value—maybe 10–20%. On a Boss 429? It can double the value.

Numbers matching affects value, insurance, and restoration decisions:

Value impact:

*Prices vary widely based on condition, documentation, and market*

The rarer and more desirable the car, the higher the numbers-matching premium.

When it matters:

• Selling to collectors
• Concours competition
• Insurance valuation (agreed value policies)
• Authentication for rare models
• Investment-grade cars

When it doesn't matter:

• You're building a driver
• Engine was already replaced before you bought it
• Upgraded drivetrain adds more value than originality
• Common model with low collectible value

How to Verify Numbers Matching:

Step 1: Decode the VIN

• Get your car's VIN from the data plate (driver's door jamb)
• Decode year, model, engine code, assembly plant

Step 2: Check Engine Block Numbers

Location: Passenger side of block, near bellhousing/motor mount

What to look for:

• Casting number (indicates displacement and year range)
• Casting date (must predate car production date)
• Partial VIN stamp (on high-value models)

Example:

• Casting number: C5OE-6015-E (1965 289 block)
• Casting date: 5A15 (January 15, 1965)
• Car production: March 1965 (consistent timing)

Step 3: Check Transmission Numbers

Location: Stamped on case (usually top or side)

What to look for:

• Transmission code (C4, C6, T-10, etc.)
• Build date code
• Assembly plant code

Step 4: Document Everything

Take photos of:

• VIN plate
• Engine numbers
• Transmission numbers
• Axle codes
• Build sheet (if you have it)
• Window sticker (if you have it)
• Factory invoice (if you have it)

Step 5: Get Professional Verification (for high-value cars)

• Marti Auto Works (official Ford database)
• Shelby Registry (for Shelby Mustangs)
• Boss Registry (for Boss models)
• Professional appraisers with classic Mustang expertise

What Breaks Numbers Matching Status:

You lose numbers matching if:

• Original engine block is replaced (even with correct-year block)
• Transmission is swapped (even with same type)
• Major components are swapped between cars
• Engine is bored beyond standard oversizes (debatable)

You keep numbers matching if:

• Engine is rebuilt using original block
• Pistons, heads, cam are replaced (internal parts don't matter)
• Accessories are replaced (alternator, carb, distributor)
• Cosmetic restoration is done

Gray areas:

• Engine bored .060" over (some consider this too far)
• Crankshaft replaced
• Block decked significantly
• Sleeved cylinders

For high-value cars, consult with registry experts before making decisions.

For Buyers: How to Verify Claims:

Sellers claim "numbers matching" often. Verify yourself:

Red flags:

• "Numbers matching" but no photos of block/trans numbers
• Seller won't let you verify numbers in person
• Numbers don't align with production dates
• Build sheet or documentation missing
• Block is suspiciously clean (possible swap)

Verification process:

1. Bring flashlight and camera
2. Locate and photograph engine numbers
3. Check against VIN and production date
4. Get independent verification for high-value cars
5. Pay for Marti Report ($45–$95) for factory documentation

For expensive cars, $500 for professional verification is cheap insurance against a $50,000 mistake.