I just recently restored a 70 GT. Replace floorboards and other steel. I used an asphault based material for sound deadening which worked well. I bought it from JC Whitney. It comes in 32 X 54" rolls and costs about $30. One roll did the entire floor. The transmission hump had already been done. If I had needed to do it, it would have taken additional material. The 32" dimension works well for the long dimension of the front half of the floor. I used 1/4" high density carpet pad, ( the stuff that is green and looks like a recycled material) over top of the sound deadening material. ( carpet stores often have small width rolls left over from jobs that they will give you. I glued that down with 3M spray trim adhesive, (only to the floorboard and transmission hump), and then glued all of the carpet pieces to the pad and steel with the same product. (available from Walmart for about $8). There is virtually no road noise present now and the carpet fit well
Jordan, I just checked the carpet on my 72 GT, and the seat frame work does not have carpet or padding over them. The carpet has a piece that goes between the rails and and small piece extends from the main carpet to the door sills. HTH.
Is the padding for sound insulation or comfort? I've got noise killer sprayed inside and will be using a thermal barrier around the tunnel area and floor to reduce heat issues. Should I still use the padding?