1963 Dodge dart bucket seat conversion

If you're going to the trouble, you might want to change strategy a little and wind up with much comfier seats with inbuilt 3-point seatbelts. Namely: the seats from Chrysler Sebring. I've seen them re-covered with period-correct vinyl and cloth materials for our old cars and they really blend in well when redone that way. See here; detailed how-to is here.