I just did covers on my 72 demon from legendary, and I had to re use my foam because it has wires cast inside it to grab the listing wires. Because of this extra complexity NOBODY makes new ones. I'm talking about the part that makes the seats dip in to be concave instead of just stretching across the outside edges, dig?
My driver's foam was a little busted, I just put in some more foam with spray adhesive to fill it out in the middle butt area. Feels good now. I've even had people tell me that the old foam is great with new covers- not too hard and new- already broken in.
Good luck
radar