I agree with 496 polara that the crossover should be closer to the end of the exhaust manifolds, perhaps just after the transmission if space allows. Let see pics of the real FF. Very special car. Not sure exhaust should be tamed, but can understand one’s desire to be discreet.
Did you make it larger than original so it would function better? It is hidden, so would make sense to me. Or were they different over the years 66-69? Maybe other years. Here is mine from a ‘69 Plymouth. Seems to be about half the size. Mine has what appears to be undercoating on it (AC car)...
Here are pics of the caps. I believe the old cap is original and was how these were done (modified by Indy mags back-in-the-day) for our 4" SBP mags. I modified the new ones with a Dremel and they fit well. One has to be careful on which deep socket to use. If you need your caps modified, let me...
I modified new Indy mag caps for my US Indy slots. The original caps on my slots were just like this. Here are pics of a new cap. I can dig out the old cap and a pic on the mag if that would help.
The short lid is the same as the unsilenced air cleaner lids from 68-69 already shown here but with the bottom ~2” cut off. They were used on 70-72 air grabber and ramcharger equipped cars and shaker ebodies using a 4 bbl in 70-71. 72 example below
Or you can use the factory short lids used on fresh air 4 bbl cars in 70-72. They are usually orange but I found this one in wrinkle black. Shows half of the stock filter.
Original rear seat covers for 1968 Barracuda folding seat. Clean and soft in light blue vinyl. Bottom still on frame, can remove for shipping. Can deliver to Carlisle. $100