Obviously if you put 305's and lighter rims of the Z/28 on the ZL1, (and maybe those brakes) what might happen to that 3 seconds? The lower splitter on the front of the /28, other stripped out items (radio, soundproofing, etc) won't make it or it's driver happy on the street. It is my belief the ZL1 still maintains the advantage over the Z/28 that the ZR1 has over the Z/28 if you added just a couple of mods to the ZL1. Advantages the Z/28 just wouldn't be able to overcome. Future ZL1's should have the better rotors and rim options and recaro's (nobody has mentioned that the recaros' are part of the 3 seconds due to driver control added).
The ZL1 remains the Most Street Capable Camaro Ever. Likely capable on the track as well with just a few mods mentioned above. Close enough anyway.