That is exactly what I am doing with my '69, (apart from my existing upholstery is decor group that I am replacing with XR7 covers from WCCC.) There is no foam as such as the rear seats still used the traditional wire frame and sprung style base. According to my research, it should be a straight swap, the listing wires are the same, but you may need to replace some of the foundation material. I believe that foam sheeting can be used to improve the bolstering. There are a couple of YouTube clips on doing this very thing. Now all I need is to find the courage to do it! Good luck with it!