It appears that General Motors currently has two types of air deflectors available for the early C4 (1984-90).

Short, Non-Reinforced air deflectors (non-Z51 cars)

Long, Reinforced air deflectors (Z51 cars)

I assumed that my air deflector was probably original equipment and since it's an 85 and does not have the Z51 handling package, the air deflector was probably the short non-reinforced version. My air deflector was pretty badly scraped and the aluminum center support bracket was snapped in half.

I talked to Jeff Kopp about getting a new air deflector and center support bracket and he suggested that I get an upgrade kit. The kit included the left, right and center air deflector sections and it included a newer design center support bracket.

I ordered the non-Z51 version and when it arrived I discovered that I had the longer Z51 version air deflector on my car! I can only assume that an earlier owner replaced the air deflector and upgraded to the Z51 air deflector. Anyway, I installed the new upgrade (or is it a downgrade kit?) on my car and the pictures that follow illustrate the important features of the upgrade kit.

Here's a shot of the old Z51 air deflector. This is the passenger side air deflector measured on the inboard side. It measures approximately 4 1/4" in height.