John,
You are right - I do agree with Weekend's comments - at least in principal. I would agree that a CLmax of 1.4 is more usual for GA aircraft, but the sectional CLmax of the Gottingen 535, at least as shown in the cited reference, is significantly greater than that of more usually used airfoils so I was content to let it run as 1.56 CLmax as a ballpark figure.
To be more precise would entail calculating the span loading to establish the relationship between peak local CL and the average wing CL - something for which I have neither the time nor the inclination.
I would say though that on reflection, taking trim losses into account, 1.56 should be regarded as an upper limit.