Need advice on a customer

They didn't make a 65 Barracuda convertible so the misrepresentation issue really isn't there.
The value on a 65 Valiant convertible, isn't very high, even if restored, so the value loss thing goes away too.

As long as he isn't making you scrounge up the parts, go for it.

We have people come in the shop asking for weird, custom things. These are the two questions we ask ourselves:

Will it diminish the safety of the car?
Will we be able to offer our standard lifetime warranty on the modification?

If the answer to #1 is "Yes", we won't do it. If the answer to #2 is "No", we explain why and leave it up to the customer.

For example: I did a custom bumper cover on an 06 Mustang. New, after-market part. I was paid 20 hours to body work the part and another 5 hours for fitting. That means the customer paid $1,250 + The price of the bumper cover + refinishing cost to have that polished turd on his car. (it was a true piece of garbage)

It looked perfect but left with a 30/30 warranty. 30' or 30 seconds, whichever comes first.