I love the late 60's Notch's and convertible Barracuda's. You may want to order the seat foam and covers, door panels, headliner and carpet from Legendary Interiors and then drop the car off at a shop to have it all installed.
Have the headliner done professionally anyway, if you are replacing yours. You can do the seats yourself with a simple set of hog ring pliers, but most people don't get them to look as nice as a professional can. They often have to add a little foam here and there to get rid of the wrinkles.
Also, make sure the car is water tight before you put in your carpet. A few bulk packs of Dynamat Extreme(about half off retail with free shipping from Amazon) on the ceiling, along the inside the firewall and on the rear wheel tubs combined with a complete covering of the interior with a product like The Insulator from Aircraft Spruce really goes a long way in making the car a lot more enjoyable to drive.