Well...I figured out the issue with unequal swing of the front power truck.
Looks like this engine was taken apart before. You can see from the pic below, the power truck "stops" are off center; which is why the power truck swings further to one side than the other....
I also know it was "serviced" because:
1. One of the drive rod connections was attached to the wheel 180 degrees off from the center of the wheel. Not sure why the drive rod was removed...the original traction tire (which is in bad shape) is still in place.
2. All 6 screws holding the frame to the shell were loose.
Plus, all the wires were no where near the motor/power truck assembly.
Thanks for all your guys' responses/help!