IMO, the '454' engine is the '$Value smasher'.... the other items (steering wheel, bumper, etc) are not bad, and would be good for most... For the most ultimate value enhancer, an original engine/accessories would be the ticket.
Sure being all original would be preferred but replacing the big block with a small block is a weekend project. And it would make the car more correct in the process, which I would think would help the value. But like you mentioned, he has to put a $$$ figure on his emotional attachment and go from there. At this point we have no clue what number the owner is thinking; he might feel the car is worth $150,000 or maybe $40,000. So Joe was going to take some time, figure out what the Z will sell for, talk to his wife and figure out just how much he wants to offer the guy and go from there.
I know selling isn't allowed here so I will ask where a good place to advertise his car might be for like-minded people to see it? Do you guys have any preferred sites? Ebay seems like a big hassle but maybe it would be the best?