Use MTL Miner brakewheels and not the Ajax on the upgrades. You also need 36" wheels in Atlas 125-ton roller bearing trucks, preferably FVM, and the bolster has to be shaved to have the car sit at the correct height (which improves the look of the car tremendously). Body-mounting MTL 1015 or 1023 takes care of preserving any etched stirrups once they are installed. Currently, there are no existing etched roofwalks that would fit the car AFAIK, but any of the CenterFlow or grain car etched roofwalks can be cut at the end platform and shortened. The existing roofwalks come out easily, but the roofs are a nightmare to remove without damaging delicate parts on the body (ladders, gates, stanchions). The roof and body are a tight press fit to begin with, but they were painted separately which adds to the tight fit.
I have no idea what color/shade the gray is by name. ESM had the plastic injection-molded in Austria and shipped here in bulk. Accurail painted and printed the cars for ESM nearly 20 years ago. Even if they could identify the paint they used back then, I would think it's unlikely they still are using the same formula even if using the same paint at this time. The roofwalk/roof components were assembled prior to painting, so this is an issue in more ways than one if etched roofwalks are installed. But it has to be something close to a standard generic light gray cement hopper color, probably the Floquil or Scalecoat light gray. Also keep in mind that the ESM cars (and paint) have aged for two decades ... so the paint color might have changed, however subtle it might be. Just gotta experiment. Feathering in the new color with an airbrush should eliminate obvious pigment variations.