Hi Ian,
I'm glad you asked, that's something I wanted to point out.
Whereas most Gamma Stirlings would have crank pins 90 degrees apart, mine are just 41 degrees apart. The angle between the displacer and piston is added to the 41 to make the entire displacer lead angle. In other words, to get the tradiitional 90 degree displacer phase lead, the angle between piston and displacer would be just: (90 - 41) = 49 degrees. I did that so that the tube between would not have to be
so long which would have added to the dead volume in the engine.
Oh yes, as you suggested, there is a slightly longer stroke on the displacer pin to help make the difference in swept volume ratios.
Make sense?
--Tim