'65 Formula S rear springs

cudamark said

Take the '68 340 intake for instance. It starts out 25XXXXX, but, wasn't until 3 years later that it was available.

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I believe the number beginning with 25... is the casting number on the intake manifold, not the number it parts book. In fact, I have a '68 340 manifold right here with me: casting #2531915