I have an 84; 456 with same problem. You remove fabric, scrape off lose foam, from back of fabric, use scrubbing brush from wifes laundry, on back. Now on where the foam still remains, on the hard surfaces, use an electric drill with a rotary wire brush, the brush that is cone shape. Put on goggles and away you go.
The foam I used to replace old one was rubber underlay, from house carpet. If you can see someone re-carpeting their home, you should pick it for nix. That is why I used it, nil cost.
Then use spray contact and glue on the foam to inside hull, then glue fabric to foam.