Why not put one of the retracts in a vise, attach the strut and using a fish scale measure the amount of pull required to move the mechanical retract.?
Factor in 40% more for safety and see if that will be handled by your servo.

I suspect you will not have problems with most medium torque servos.

If the mechanical retract does not bind anywhere, very little force is required to move the retracts.

The mechanism locks, at either extreme, so as long as the servo holds the mechanism in place the mechanical retracts do not put strain on the servo.... only during servo movement.

What "gets" you with mechanical retracts, or any retract for that matter, are things like debris or metal particles that can lodge in the wrong place preventing arm movement or actuator movement.

I see some people claim that pneumatics are far more reliable, but IMHO if both are kept clean with free movement of the mechanism, operational reliability should be about the same.