The 707 and KC-135 are similar in many areas, but they are indeed very different aircraft when you begin to consider the details. For example, the fuselage diameter of the KC-135 is slightly smaller than that of the 707. The wing of the KC-135 is shared only with the 707-120, all newer versions have an improved wing. The KC-135 also carries a lot more fuel, up to 209,543 pounds in 10 tanks.
The biggest thing that I would love to see is a detailed cockpit and accurate systems modeling. If the developers need any help I would be more than happy to help them with the technical details of the systems.

I know that I'd be willing to spend a lot of money for a good KC-135 model, but then again, I flew them for a long time.

Picture of cockpit:
http://www.airliners.net/photo/USA---Air/Boeing-KC-135R-Stratotanker/0364499/L/