if I'm following along, which is often not the case you are trying determine is the trailing arm mount flanges have been bent? consider on of these;;;
you don't have to get one of the fancy digital ones, simple old school units can be had at a hardware store for < $10. check the angle off the torsion tube to the outer mounting flange on the perceived good side vs the perceived bad side. you will have to hold it level in the t-tube, capture the angle of one side, torque down the stop and check it vs the other. for at least the outer flange you won't even have to pull the trailing arms. id have to think on it some, but I bet you could measure to the inner mounting flange location by pulling off your new tool at 90* and measuring.
id think if it was impact from the side pushing the wheel inward would cause more damage to the outboard mounting flange at it's base, and the inner flange more towards the end. right?