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3S is a known Canadian Suffix for 1968 L36.
We’ve looked at this 3S also other Canadian Numerical Suffix Codes in past threads, I have an old Non-GM publication that lists a bunch of them so anyone check in if more pop up.
Also of note, Canadian car Vin Plant designations are also numerical unlike US built cars, Plant 1 = Oshawa, 2 = St. Therese as this example etc.
:beers:
~ Pete

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68 Biscayne
 

Does T = Tonowanda ?
0111 = Date Code ?

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Yes, standard Tonawanda build/Date format but unique Canadian Suffix beginning w/ a #.
Also of note, often the same ones were used w/ different Trans and other Options where a US car would have a specific Suffix for Auto/Stick etc.
:beers:
~ Pete

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