I had 2 of the Atlas diecast cars, that came in 2 rail. these were fishbelly 2 bay hoppers like the Western Maryland had. I found them way too heavy. I eventually parted ways with them The MTH Fishbelly is as good or better a model and weighs less than a lb. the Atlas diecast weighed 2 lbs as you mention.
I find diecast too be too heavy, and the detail is often too thick when compared with injection molded plastic or etched brass.
But if you like them go for it. These cars did come before Lionel was even hinting at the scale guys, so I am guessing they do not Kadee couplers mounts. But you could add a pad, and drill and tap it. Or the bottom of the car may be in the right place and you can just drill and tap the diecast. If it is good material it will hold the threads well, just don't horse it too much, do everything manually, not with a power driver. A 2-56 screw works just right with the Kadee couplers. I think a #50 drill is the tap drill for 2-56.