If you're looking for a cover that goes over the top rail of the bedside, no one makes them for the older long stepsides. The only thing I saw from Mar-K are plugs that go into the stake holes. I had to custom make a set for mine
http://rides.webshots.com/photo/2143877990092261295Fvdwnc. They're brushed stainless, but they could be made from diamond plate or polished stainless if you wanted. Check with a local sheet metal shop, they can make them for you. BTW-not to nitpick, but the '56 would have a 7 1/2 foot bed. The 8 foot bed came out in mid-'57.
