The older Eliminator cars did use a MT plug door 40' box car. I also have one of the orange cars and it is getting an undec shell with a coat of silver paint and ATSF MW decals I believe the current cars use a Atlas shell.
I've had pretty good luck with my modified Centerline Products track cleaning cars. My track cleaning train consists of a N2 with a brightboy insert and a D12 with the handy wipe roller. I use the handy wipe dry. As you can see in the photo below, the brightboy is not weighted in the car. If you need additional cleaning, you could add the Centerline Products roller as a weight for the brightboy. For heavy jobs I prefer the Walthers CRATEX abrasive cleaning block part number 949-522.
Now that is a pretty neat idea putting a bright boy in the N2 and being able to use the roller as weight. Thank you for sharing that. I have an N2 but don't run it much because I don't like dealing with cutting a applying the handi wipes all the time. Think I will get my N2 out this weekend and give that a try.
John, I don't have any of the Aztec cars you mentioned but can highly recommend the CMX Cleaning Car if cost isn't prohibitive.