Dynamite article Jack!
I've, like a lot of car club members, been in a similar situation and have gladly given of my time to help friends with projects more like the Weissrat Chronicles. I have a lot of parts in my shop that landed there by some force and await someone else's need. My shop is just that sort of Hot Rodding trading post.
In your example many years passed, and the Little Red Hen got a lot of use out of the vehicle before the value skyrocketed. So I ask myself, if the car was sold much earlier, say after 5 years and it sold for no more than any other used car, does the little red hen owe anybody anything? I say no, Presuming she said thank you to those involved in the first place, it's just good manners, she owes them nothing. So, after the car sells for a ton, I still say she owes them nothing. That said: If I were in that situation, I would find some way to give them something more than a hearty handshake, because in my soul, that would be the right thing to do.
My thinking would probably go along some sort of line; regarding the cost of parts and the price of their labor that went in at that time and a just compensation for that.
For myself, while working on someone else's project, much like in the Weissrat Chronicles; I want to be a part of it for the experience. I don't need any sort of compensation. If someone feeds me and I get to have fun, doing something really silly, involving welders, mills, lathes, hammers, tongs, lions, tigers and bears... What more do I need?
Regarding the Porsche: I agree, I hope he sells it also and goes on a wonderful adventure! How cool would that be? I also hope he continues to learn throughout his life and never stops playing with mechanical devices and is never afraid to help a friend out on a project. I know too many who get far too stuck on their own compensation (seeing the tree) to see the potential of the experience (missing the forest).
All of that said: Jack; if you find yourself in need of parts for something decidedly more American made, feel free to wander through my shop; you never know what you might find? 🙂