Just so you know, 66 Cuda and Valiant buckets are the same as 67, just the tracks are different! The 65 and earlier seats are completely different, as are 68 and later! I have some 66 Cuda seats, but I'm in Michigan and that's a lot to ship!!
Very close but not exactly the same... The upper member of the 66 seat back frame is still round like earlier. This puts it about 3/4 inch taller than 67. For 67 they reformed that member to square and stamped holes through it for headrest posts. All this effects the fit of a 67 skin on a 66 frame. The finish binding of the skin will peek out from under the metal seat back at its upper curved corners.