65 barracuda exhaust
63-66 Valiants and Barracudas have a two inch shorter wheelbase than 67-later Barracudas and Valiants. (Excluding Dart bodied Scamps, which have a Dart 111 inch wheelbase.) The increase is all ahead of the trans crossmember, so engine to rear end distances are the same, early or late. Like 66fs, I have a 71 Duster 340 driveshaft in my early (65) Barracuda.
The early A engine compartment is narrower, so while the 67-up exhaust will fit without modification from the trans crossmember back, inside the engine compartment is another matter. However, early on, I ran a 72 right (passenger) side 340 exhaust manifold, and a stock 71-later Duster 340 exhaust pipe fit perfectly after I cut the pipe after the first turn off the manifold - where it turns to the rear then levels off before turning back down again - and welded in a 2-inch or so extension. Later, when I switched to 68-70 hi-po passenger side manifold, I had to just make a new pipe between the manifold and the trans crossmember.
On the driver's side, pretty much nothing other than the manifold flange was usable. I cut the pipe a couple inches below the manifold outlet, ran a 2.25 inch pipe down between the torsion bar and the frame and then back, to join a 71-later 340 left side exhaust pipe somewhere ahead of the trans crossmember.
From the trans crossmember back, the Walker replacement Duster 340 exhaust pipes, mufflers and tail pipes fit perfectly, except I used 69 Barracuda chrome tips instead of the long Duster tips. I did have to cut an opening in the right side of the valence to match the factory 273 hi-po opening on the left side.
So, I would think that most of the Summit 67 Barracuda system would work, but you'll have to modify the engine compartment portion of it.
By the way, I never even cut the trans crossmember until I put TTI headers on it a couple of years ago. Just ran the right side pipe under it. Here's what it looked like pre-header exhaust with the pipe running under the uncut trans crossmember.: