I've completed the addition of two larger, more powerful motors (twice the torque of the original servo motors). The files for the changed parts are available on this site.
First, I added the aluminum servo horn to the new shoulder axle.
Next, I disconnected the existing elbow joint.
Now, I set the new motor and bracket in a similar position to the old--so I wouldn't mix things up too much.
I mounted the motor to the upper leg.
I attached the aluminum servo horn and back bearing to the ankle servo connector.
I attached this assembly to the lower leg.
I attached the lower leg to the elbow assembly.
I pushed the shoulder axle through the linear bearing and attached it to the upper leg motor bracket.
I attached the servo horn to the servo motor and tightened the locking screw through the hole in the axle/shaft.
I checked the total leg mass and it came in at 986 grams--which is 86 grams more than the original.