For many years I was measuring these cars and it took time. My son built a fixture and now we can set a car on to check them or build a body from the rails up as pictured. Found many crooked cars that were never damaged when they were set on this fixture he made. We found some cars were built crooked.
Once the car is set on, There are legs to bolt where the bumpers fit. If they are bolt in place the car is straight. The front bumper legs are thick steel and when bolted fast they straighten the frames if they lean as yours are