If the link works, this is a follow-on project based upon the 1982 GM Aero 2000 ( Epcot ), 1983 GM Aero 2002, and 1984 Chevrolet Citation-IV concept cars, Cd 0.23, Cd 0.14, and Cd 0.18, respectively.
A guess for the 1987 variant would be in Cd 0.13 territory. So far, it hasn't been reported, and no confidence that it ever will be.
As with all concepts, one must take into account whether they were 'running' prototypes, or, simply 'gliders', with no engine, powertrain, cooling system, etc..
Also, electrification of these cars could allow actual Cds to approach those of the non-operational concepts, as cooling systems would only be sized for around 30.8% of an ICE.
Synthetic vision could allow a virtual 'mirror-delete.'
'Cooling plates' could supplant what's left of the radiator, leaving only a small porosity requirement for air conditioning condensers.
https://www.google.com/search?q=1987...gKDKiUgbfAh_OM