1976 Chevy Monza 2+2 aero mods
 

Here's a little article about a Chevy Monza with Chevrolet Racing Division fiberglass body kit which lowered the drag from Cd 0.40,to below Cd 0.304.
Customizing a V8 Chevy Monza: By Bob Gumm
With the kit,the Monza gets the Cd of a 2014 Cadillac ELR.:)

The wide-body kit adds maybe 2-4sq ft to the Frontal Area. That's 10-20%. The line drawing doesn't show rear view mirrors.

side mirrors
 

The kit is only intended for dedicated race cars.Some rule books at the time may have allowed for certain SCCA categories which were 'mirror-free.' Not sure.