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Decode your 65 66 67 68 69 70 Mustang Engine Block
By: fastbackstack ( 5369Feedback score is 5,000 to 9,999)   Top 1000 Reviewer
438 out of 449 people found this guide helpful.

Classic Mustang restorers who are looking to restore a vintage Mustang to concours condition will need to understand how to identify the casting number and date code number on an engine block.  Matching numbers are important to collectors.  The correct casting numbers ensure the Mustang is rebuilt to its original condition and has the correct numbers that would have been assigned at the factory years ago.

This guide is written to help you determine what numbers to look for when accurately restoring your Mustang.  Please remember to indicate below if this guide is helpful to you.


Where to find the engine block numbers:  look toward the back of the engine block on the right hand  side, above the starter. You will find the casting number at this location. 

For the purpose of explaining each individual letter and number, we have created a sample engine block number and date code.  Then we have broken these numbers down, explaining what each number and letter represent.


C - Designates the decade that the engine block was made.

C = 1960's; D = 1970's; E = 1980's and so on

5 - Designates the particular year that the engine block was made.

5 = 1965; 6 = 1966; 7 = 1967; 8 = 1968; 9 = 1969; 0 = 1970

It is important to note:  a more accurate date of when the engine was made is reflected in the date code which follows the casting number.  Casting numbers were sometimes a year or two ahead of the block's date of manufacture (sometimes they were even behind the date of manufacture). 

This is evident, for example, in a 1964 1/2 Mustang with a 289.  The casting number "C5AE-6015-E" and the date code "4D17" show differing years of the engine block's manufacture date.  One might think that "C5" indicates the engine block was made in 1965.  However, according to the date code, it was actually manufactured in 1964.  Always look to the date code for the correct manufacture date.

A = Designates the vehicle the engine was designed for. 

A = Galaxie; D = Falcon; F = made outside the USA; G = Comet; J = Industrial/Marine; M = Mercury; O = Fairlane; P = Autolite or Motorcraft; R = Rotunda; S = Thunderbird; T = Truck; V = Lincoln; Z = Mustang

E = an engineering number used by Ford
(The 289 was originally designed for the Ford Galaxie and the letters AE stayed on the engine block number even after other models were added to the lineup)

6015 = Designates an engineering number used by Ford. 
"6015" meant "289 Engine Block"

E = Designates the location that the engine block was made.
Engine blocks were made in Detroit, Michigan and Windsor, Canada


The next set of numbers, "7C20", indicate the date code.  In this example, even though the casting number reads "C5", it doesn't mean that the engine was made in 1965.  You would need to look at this date code to see when it was made, which in this case is 1967. 

Breaking the "7C20" date code down:

7 = designates the particular year that the engine block was made  (remember to look at this date code for an accurate reading of the engine block's manufacture date)

5 = 1965; 6 = 1966; 7 = 1967; 8 = 1968; 9 = 1969; 0 = 1970

C = designates the month that the engine block was made

A = January; B = February; C = March; D = April; E = May; F = June; G = July; H = August; J = September; K = October; L = November; M = December
(the alphabet letter "I" was not used in the sequence)

20 = Designates the day of the month


In summary, our engine block sample number "C5AE-6015-E    7C20" tells us the following: 

At first glance, one might think that this is a 1965 Galaxie 289 engine block.  However, according to the date code, this engine block is a 289 block made on March 20, 1967.

Ideally, you would want the engine block date code to be 2 - 6 weeks BEFORE your car's build date.  If you had a car that was built June 1, 1965 and you found an engine block with a date code of 5E10, which is May 10, 1965, this would be a match made in heaven!

Good luck deciphering your dead Mustang scrolls (not to be confused with the "dead sea scrolls", although I have a few Mustangs that look as if they spent some time on the bottom of the ocean)!

If you have found this guide to be helpful, please indicate so below by voting "YES" to this guide.

Be sure to check out our other Mustang Guides for additional restoration information and helpful tips.

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Copyright 2007:  FastbackStack, LLC

Guide ID: 10000000003222033Guide created: 03/28/07 (updated 04/04/15)

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