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I recently acquired what I have determined to be a 1964 389 GTO motor. The engine code indicates it to have been from an Automatic tranny, and a 4 barrel carb.

Engine codes as follows: 79J 408363

Heads - Only numbers I can find are located on tags that are attached each by two pan head machine screws with the number "76" stamped into them. One each sits on the rear driver's side exhaust port, and the other sits on the front passenger exhaust port.

Anyone have any idea which heads these are. They don't have the stampings I've seen on others '64 389's.

Block & heads are painted what looks to be the original silver/blue metallic.

Thanks in advance for any help you guys can give!! :cheers
 

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76 coded heads were used in 1965 for a 389, HP ratings of the engines was 290,325 and 333. Valves were 1.92 and 1.66 and the C.R. is 10.5.

They were also used on the 1965 421, 338 HP, 10.75 C.R.,
 

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The heads may be service replacement heads if they have an ID tag attached to them. Factory assembly-line heads used casting numbers to ID - not tags. I have seen the tags used for SR components since "generic" castings were used to make several different heads for the SR components. There should still be a casting date located somewhere in the area under the valve covers, and this may provide a clue as to their origin. It's quite possible that your '64 engine received some service replacement heads in '65 or '66 - there's probably a good story hidden there somewhere...

The silver-blue metallic is not the original color for a '64. The silver-blue was first used in 1966, and may be another clue as to when the the SR heads were installed. Correct color for '64 and '65 is a non-metallic Robin's-egg blue.

79J is the engine code for a 1964 389 325-horse (4-barrel) used with a 4-speed. You should still check the casting date to verify.
 
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