The concept Black ZL1 shown (2 created, potential COPO 9787 assigned but never factory-built) was Piggins' attempt to get more volume, but its likely $9,000 tag was the final killer.
COPO 9560 (ZL1 engine - 69 built) + COPO 9737 (Sports Car Conversion Pkg, created for Don Yenko but orderable by anyone) = the closest thing to a ZL1-Z/28. Exactly TWO of the 69 were ordered (#3 - Berger, #69 - Huebner). Z/28 15" Rally wheels/tires, suspension and 140 mph speedo were included. Curb Weight similar to Z/28.
Curiously, NO Black COPO 9560s were factory-assembled. Tuxedo Black was "restricted availability" before COPO 9560 "volume" production commenced and then discontinued after April 1st (no fooling).