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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.
~ Pete
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