I'll have a somewhat better idea as I get through the lists. I am trying to compile a roster of cars to represent the district with a focus on the setouts and pick ups at Waterloo. But like most RR projects, it's hard to stay disciplined. I just found the other day a block of ATSF stockcars that were not a common occurance (at least not in '65) but with IM coming out with what would seem to be the appropriate car, it's hard not include them. I have started a list of druthers when it comes to rolling stock by picking out interesting mid-west roads that repeat like MNS, DMIR and FDDM. But, of course, I can't even find pictures of some of these cars. I was hoping to be able to do this with a couple hundred freight cars using four 40 cars trains (nos. 41,42,43,92) and 40 other cars for Waterloo. But that is way too restrictive. I'll probably end up with 20 cars per train that are 'generics', 10 cars for setouts, and sets of 10 cars that can be put in the train that shouldn't always be there like autoracks/auto parts, covered hopper blocks (TLDX), stock cars (ATSF and CGW), one wreck train and blocks of asphalt to name a few.
Of course, if I purge my MT collection of 40' standard box cars with a build date prior to '47 (before the ps-1 came out), that should clear a lot of space.
You'll probably see this thread back in couple months as I'm able to pair down the roster. At that point I will speek more to why particular cars were chosen which maybe could be useful for you in the big picture.
Jason