[LS short box]

Here's a thought don't know if will help but take some very detailed pics of the cab and show them to different body shops in you area. If one or more show any interest offer to pay them to come out to look at it. A seasoned body man for the hours and painter for the material costs should be able to give you a real close estimate.
One more thought is contacting your local car club (if you have one) and see whom they might recommend.