As you already figured out, there is no angle constraint block in SimMechanics 1G. In the first generation you could connect a Joint Sensor and a Joint Actor to the revolute joint. Then you can use the information about the position (and possibly of the torque) to calculate the torque needed to enforce the ranges. Using the Joint Actuator you can apply this force to the revolute joint. Keep in mind, that depending on the implementation of the controler, the system might get very stiff.
So generally I would advise to update to the second generation of Simscape Multibody since it has a easy solution for this issue and is also updated regularly.
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