Layson's has some that are close-ish. I replaced 3/4's of my floor pan with them. They're definitely not for '64 Valiants though. They have a weird kick up on the outer lip that doesn't exist on the '64s. I ended up making small slices in mine all the way around with a plasma cutter and beating it into place with a hammer. They do the job, but they're really not much better than if you used cardboard, cut your own steel to match, and have the ability to add the strengthening welts in the middle. (There's don't match factory anyway.)
If you do want to use them, they have a fall sale going on now for 20% off. I think there's a code or something. They've probably posted it in the vendor section.
