What your OB said about not being able to tell from x-ray is true - X-rays don't allow for the movement in your pelvis that is possible towards the end of pregnancy, nor the ability of your baby's skull bones to over ride each other as your baby comes down. Also, if you're in an upright position for birth, this allows you to take advantage of gravity.

28 years ago, the advice was very different, so I can see how your OB was dismissive. If nothing was written on the actual report, there might not be anything significant on the actual X-ray - ie, the chiro might have been talking more from opinion, than observable fact.

The true test is to go into labour and see what happens. If things don't progress, you have your answer. I guess the question is really - do you want to labour, or do you want to have a CS? If you want a CS, that's ok. If you want to have a vaginal birth, there's no reason not to plan for that.