Canadian poncho engine ##

Hey guys,
looking to see if anyone can point me in the right direction. Picked up a 70 formula firebird but she's of the canadian pursuasion. Engine number is 668875 over x4. Anyone know what this means?

 

if x4 is the code stamped on the right front of the block, its not the original 1970 engine.

http://www.pontiacpower.net/engcode01.html

 

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