stainless steel brake lines

never used and sold car 100.00 /obo for 68 a body think this will work from 68-70 ply?

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Darts and Barracudas had different wheelbase in 1968. So, short answer is maybe. Could they be made to fit? Again, maybe. Trying to find 3 extra inches in Barracuda lines to fit a Dart might be troublesome. You could cut and insert a splice to get the extra length.
Like abodyjoe said, find out what they are supposed to fit and go from there.