Ford Ranger rear end fit '71 Dart?

CudaFactHackJob said
I see "how to" weld spring perches; and an angle level is always used to get the perches at the exact angle. But I NEVER see anybody use a straightedge with a bend in the middle to make sure that the perches are parallel to each other side to side. If the perch is cocked sideways, the rear end will move sideways as the spring deflects.

I understand a straight edge would be the most accurate but a straight edge to do that task isn't easy to come by. In fact I haven't seen one. Can't you do basically the same thing by turning the angle gauge sideways to verify the perches are parallel