You are in Luck.One of my other hobbies happens to be building model airplanes. In the book, "The B-52 Stratofortress in Action from Squadron-Signal Publications shows a picture of the car. It appears to be a three unit Articulated car built from old heavyweight baggage cars with a special built center section.
You can optain this book by sending $14.70 (Post Paid) to:
Sqadron Mail Order Hobbies
1115 Crowley Drive
Carroliton, Texas 75011-5010
Catalog Descriton is "B-52 Statofortress in Action"
Item number is 7-SS1023
I have also briefly discussed this matter with my father. We both think that writing the Department of the Air Force and ask them for a copy of engineering drawings for the cars and giving them a brief description if why you want it might get you a set of plans to work from to build a model.
Thank you for posting this question and I am glad I could be of Service.
Sincerely
James R. Mitich