Stirling engine of gamma type

It's simple design of a Stirling engine of gamma type, made on SolidWorks. I have originally made this project for a high school project, 5 years ago. This engine was totally functional, and work very well if you put it on a coffee cup for example. But after a Matlab simulation, the yield was a little bit under a normal yield for a 3D printed Stirling engine. So feel free to improve it!
I have by inadvertently lost all the pictures of the original engine (who i have let at my high school), and i have no remade it since; it's why there is no pictures available.

I used simple wire to make the rod, a piece of balloon to make the piston, and a piece of extruded polystyrene to make the displacer.
The hot plate and cold plate was made in a 2 millimetres sheet steel.

Sorry for the English mistakes, I’m French...