It is a mistake in the paper work. A fluke, that is all. When you look at the order form when you check Z28 it automaticly picks the engine for you. GM DID make a V6 with the all the Z28 options, it was called a Y87 car. NOT a V6 Z28. It would make no sense to have a Y87 car and a V6 Z28.

The top dog in the 2002 V6 world is the RS/Y87.

The biggest issue with the paper work is it says Z28 on the top BUT the Z28 code does not show up on the paper as a installed option. It should be a code just like F41 or G80.
I am pretty sure the Z28 and the Y87 both came with the F41 handling package and G80 limited slip should not have been listed seperately, but I could be wrong. It is ashame it is not a Y87 car, that would help the value. Currently it is just a well optioned V6.

 

Unless your friend has the only v6 z28 in the world. Put it on eBay for $100,000 see if it sells.