you should know it when you hook it up....if you set the rod to say about a 1/8" of tension on the arm and the boost goes to 17-18#, then it is a hd model..
If you have the old actuator, and a fish type scale for larger fish, you could pull them both the same distance and see if one has a stiffer spring than the other.
If you have the old actuator, and a fish type scale for larger fish, you could pull them both the same distance and see if one has a stiffer spring than the other.