Hello

I am building an ltd stirling engine which will be able to run off of the heat from someone's hand. I am basing it's finished size on a 140mm displacer piston. I would like to know the relative thickness of displacer and displacer chamber (i.e.the stroke of the displacer) and the stroke and diameter of the power piston for optimal running at this temperature difference. It would be great if someone could help me in this area.

Thank-you
cnc kiwi