Thanks for the assist Guy! The first image you linked to appears to have created a hot-link conflict and will not show.
The other images are in view.
The "Air Stair" feature for the forward access door is not featured on the old Aurora kit, just the outline of the door and according to my research efforts it was not fitted to all DC-9 aircraft. The rear steps are what I am after. The rear view does help some in establishing the width of the thing and I can do some more guesstimation on where it lies on the underside of the fuselage.
Without getting in to too much detail. The objective is to try and scribe in the rear access stairs or if possible create an open step feature for an "alphabet agency" clandestine cargo aircraft that could drop "stuff" at night or in adverse weather. Based on something I read several years ago that I think was a B727 that had the rear stairs modified to create a ramp to allow delivery of small "door bundles" with parachutes in support of some guerilla war. So with that in mind, I hope to create something similar from the DC-9. It has no windows along the fuselage sides so it is almost ideal for a cargo carrier.