My 59 fleetside (original wood) had one and we recommend it as cheap insurance. The stainless ones actually look pretty nice under the wood. Kind of a purposeful blend of form and function. Mar-K makes two sizes in both steel and stainless, http://www.mar-k.com/various_restoration_items.pdf as the trucks used a larger shield after 1973. You don't want to find out you needed one when the wood starts smoking.

Mar-Ktech