I refurbished an XT recently, including sanding and repainting the internal plates, replacing the foam layer, and installing a Teensy and Soarer's Converter.
For the paint, I used Rustoleum Universal Satin Black (primer and paint in one). I applied three light coats, with wet sanding (3M 400-grit wet/dry silicon carbide) in between coats, allowing 48 hours drying time for each coat. Before applying the first coat, I sanded down to the bare metal. For the foam layer, I used 1/8-inch silicone sponge. The foam was tight, and it took considerable pressure with a long bar clamp to get the plates to slide into place.
In any event, everything worked, and I am very pleased with the result. I smile every time I use the keyboard -- the notion that a 30-year-old PC keyboard could work with a brand new Mac Pro computer is some kind of sweet poetic justice.