All the air boxes came with a heat shield, unfortunately they are still about an inch short of protecting the plastic box from the jet blast of a failed oem joint gasket (happened to mine in about '88-'89) or a poor fitting aftermarket 'slip-on' muffler.I didn't even see it either when I bought the bike. When I replaced the airbox with an Ebay unit, the new one came with a metal plate mounted to the box right in that spot that the original either didn't have or lost at some point.
Our fearless leader Tom Schmitz, aka Souperdoo has the fix tho,
click here--> Post Page
He has lots of great stuff on his personal site!