The SS is no bargin but would be my choice.

The Z is not real or if it was is no longer for mis matched parts. $100 says its a fake anyway

 

Fake, I like the Z-28 but would not pay what he is asking for it
Check the cowl tag on the SS and verify if it is an SS or not

 

I checked the cowl tag and its a legit SS

How can you tell the Z is fake by the picture? I don't disagree with you, just curious what you see

 

My first clue would be the price. A numbers matching Z is going for over $100k. My neighbor that just sold one he had two buyers jumping at $100K and ended up selling it to a guy in Washington State, unseen, for $104k.
Does the Z have any documentation?
Z's can easily be cloned with all the parts available but the real truth is in the VIN number and documents.
Just my opinion but I'd go after the SS

 

The price
Worth 175, if documented well, like with a dealer option sheet and other dealer sales purchase papers