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I believe the front fenders/grille panels were painted separately and then assembled to make the front clip so all of these bolts would be natural. The 8 bolts holding the front clip to the cab/chassis would also be natural.
I also think the rear fenders were painted and then bolted onto the bed. What make me thik this is the piece of bed side that's under the fender is always the body color, so the bed sides must have been painted before the fenders were installed.
Here's a 1956 factory picture with a Chevrolet front clip being assembled...
http://www.imgrum.org/media/984897942868241686_367957858Mike B
