When I built Caroline's Truck I thought about all the things I could do to quiet these nice old trucks. This came to mind. You can find rubber at any rubber supply house and I ended up buying some 2'' x 4' dense rubber about 1/4 -3/8'' thick, to help solve my thoughts. The cost is minimal.
place a piece about 2'' square under each bed support top and bottom of the wood piece. I made my wood blocks from hardwood, not the stuff you buy from AD suppliers. A glob of contact cement helps hold it in situ while you assemble the final fit. the long bed bolts slide right thru the center hole and the pressure holds the rubber quieting in place.
place a thicker strip about 14''-16'' long under the CAB front support to the frame.
http://s67.photobucket.com/user/1951otter/media/9A-3.jpg.html?sort=6&o=306http://s67.photobucket.com/user/1951otter/media/64040020.jpg.html?sort=6&o=304
