My experience with the seats makes me totally agree with John and Ray. I bought the high dollar preformed foam and a complete set of covers from one of our vendors. After trying to put one of the old covers over the new foam, to make the car driveable during restoration, I realized I was NOT going to do the install of the new covers.
I found an upholstery shop that specializes in classics and roadsters and decided to let them do the install. They had to modify one of the seat covers and ended up reshaping all of the foam. I had negotiated a price for the initial install, but neglected to renegotiate for the modifications.
Bottom line is the install nearly doubled the price of what I had in the foam and new covers.
After that I would highly recommend finding a good upholstery shop and let them make the covers and foam, and then they are responsible for the entire job. My friend did that on his TBird and ended up paying a lot less than I did and got a really nice job.
Just thought I would share my experience.