Megan, I had exactly the same idea when I woke in the night. There would have been imprints of the cables and copper flash residue on the aircraft, so the investigators would have been able to state with certainty the angle of the aircraft with respect to the cables. Any of the cable strike marks would be sufficient. It is so obvious, there was no need to explain it in the reports. The marks would have extended beyond the leading edges of the wing and/or fuselage so there would certainly be clear evidence of angle of contact. We know that the cables were carrying power and that a blue flash was seen by witnesses.
I don't know quite how litigious the US was at that time, but I suspect that whoever maintained the power lines would have made an insurance claim against the airline to repair the damage. The insurers would have insisted on full details of the damage and costs of repairs down to the last penny, judging by my dealings with such companies.
The other point that I missed in looking through the mass of documentation is that the two official reports are, in fact, merely summaries of the investigations carried out. A huge amount of detail has been skipped or glossed over because it wasn't directly relevant to the cause of the accident or avoidance of further problems.
The actual investigation documents would have filled many boxes. What has been published is just the highlights. It may well be that there is an archive in a warehouse somewhere containing all the documents generated during this investigation. That would be a treasure trove to find.