Lemme get this straight (and I didn't read any further than the first page)
You did work on a car, and unless it TRULY increased the value of the car (Nicer motor, more correct resto, major repair, etc) you expect to be paid for it?
If you don't have sentimental value to the car, work with the guy. Or at least meet him. He may be OK with not buying him once he sees it.
Remember, the people that will spend huge dollars on these cars are dying off. You're at peak selling price to make money and it's going to be downhill from here (for the most part). It's not special enough to be super collectible.