thanks for the ideas and info.
answer to truckernix, yes my 51 is a dually, the VIN lookup says its a 1-ton model 3800. I might be wrong in thinking its the oversize fenders - thought I read somewhere where the 1-ton is oversized -- they look like it. below is a link to a picture of my truck (I have not figured out how to place it here on the post).
http://geocities.com/gocountry99/