[Fixwhataintbroke]

Unless I'm mistaken that's an 83/84 single headlight setup. I used LMC as a reference http://www.lmctruck.com/icatalog/cc/full.aspx?Page=41, you'll notice on the lmc picture that the 83/84 has 3 fins top and bottom going horizontal while the 85-88 only has 1. All pre 80 can be ruled out because they are round headlights, and the 80 rectangular use narrower turn signals just like 79 round, and 81-82 the single headlight models has the bottom section covered.