Just sayin', from what I recall the ZL-1 and Z/28 are more "related" perhaps than they are different....
...The ZL-1 as it is now known, was slated to become the Z/28....
....If the Z/28 wasn't what you had hoped for when it debuted, you were steered towards the ZL-1 to get what you thought you were missing...
Both different models, now of course, but actually considered more complimentary and optional to each other initially...