You can find replacement carpeting for your 1973 Ford Pickup here -
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Blake and I will show you the replacement carpeting that we're installing in our 1973 Ford F350 Super Camper Special Pickup. This installation process would be the same for 1973-1979 Ford Pickups, but would essentially be the same for any vehicle, though. Once the old carpet is removed, clean the floor, and then lay the new carpeting in and let sit for at least 24 hours. This will allow the carpeting to retake it's shape. Never, never lay the carpeting in the sun to warm up. The heat can cause it to lose the moulded shape, turning it back into a flat piece of material.
Once the carpeting has been in the vehicle for at least 24 hours, start working it from the back to the front. You'll need to cut out any openings for seat mounts, seat belts, floor shifters, etc. Make sure the carpeting is aligned side-to-side before cutting your holes.
Take your time, and usually in an hour or so (depending on the size vehicle you're working on), you'll have the new carpeting in, and the vehicle looking like new again!