What size head pipes and tail pipes used on the factory '68 340?

dibbons said

Would like to know what the original cars used, diameter wise, before considering these manifolds for one of my project cars. Thank you.

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The 1968 340 Darts and Barracudas were equipped with 2” headpipes and 1-7/8” tailpipes. In 1969 they changed to 2 1/4” headpipes except for the left flange pipe which was 2” for about 18”. The tailpipes were also 2-1/4” out of the mufflers and then changing to 1-7/8” about halfway back.
Hope this helps.