If I am not mistaken, the hood pad with the heat shield was originally installed on 1986+ SD and SDLs. As these engines had the dreaded "TRAP OXIDIZER" which produced an enormous amount of heat. Being mounted on top of the exhaust manifold it was very close to the hood and insulation blanket. I wouldn't be surprised if the heat shield was installed so as to prevent a fire if the insulation blanket were to touch the TO.
I guess the metal would also help 'spread' the heat so as not to burn the hood paint too.
My $.02.

Bill.