I don't see 'Z28' in that picture (I have the book, no scanner). Looks like it is just an intermediate design from when they were trying to figure out the design of the rear end. Look at the orange car in front.
Note, if I've gotten any facts wrong in the above, just ignore any points I made with them
don't believe a thing you read about the next gen Camaro -- as history has proven time and time again:
WE DO NOT TALK ABOUT FUTURE PRODUCT PLANS PERIOD FbodFather
Camaro5 Fest sub-forum