Very cool Brian. We studied Sterling engines in my collage physics course. It must be a great feeling to be able to make a running engine from parts you made yourself! I also think it was quite clever of you to power yours with compressed air! Have you done any stuff with model planes? I saw a great project a Guy did making a scale version of the Spruce Goose which he powered with appropriate scale engines, and I believe it did fly. I'm pretty sure the Guy has passed away now, but I know there are still web sites about his project.
I know what you mean about burning out on projects, and trying different things for a break. We spent 12 years fixing up our old house, and adding an addition to it. Mytruck project is the change I shifted into. I still really want to make a wooden tall ship model, some time in the future, maybe after the truck gets done. Glad you still are driving your truck daily!