CT20b & CT26 Actuators Same or Different?

Seen both and looked the same. I don't know if the wastegate spring is internally is the same.

IMO don't waste your money with a second hand wastegate actuator regardless of gen. Buy new kinigawa or mamba or aftermarket where you can add different wastegate springs for different psi and most importantly has a new diaphragm for longevity - for the low cost it's the way to go.

The rod length and body remains the same. As for the diaphragm / rate, testing has had then similar - use google / mr2oc.
Beginner enthusiast self proclaimed engineers have measured rod travel under different psi. I have not come across someone who has tested both under the same conditions, so individual tests / measurements is unlikely to be accurate in comparisons.
Hope someone can help you further,