Welcome and enjoy your Valiant. Whats wrong with interior? Stock interiors (carpet and simple things), Legendary has good stuff. Herbs auto, Vans auto.
I would not try a bow headliner pay for it they are tricky. Guy here does nioce work for 300 and thats nothing compared to the headache they can be. SEM interior colors and dyes (follow instructions) Fat mat for cheap sound and road noise reduction. You will find tons of answers on here. Watch adds on here for things you need. All this is if your car is mechanically sound and up to par. I would get new seatbelts, disc breaks, good suspension, motor tune, hei ignition. Things that will make it a more enjoyable ride first. Dont want a nice interior and have it sit in the drive way. Oh and get familiar with valve lash adjusment and drum brake adjustment. To save money. These are great cars. Gotta love the first ride mine was a 72 Ford Maverick. It was ugly but i was as happy as a pig in crap! Have ya named the car yet? If your looking for parts I believe the 1963-1966 are interchangable have FUN couldnt ask for a better first ride.