You might do better to order up some of the Canadian Pacific 33 foot hopper "runner packs" from MTL that are coming mid-next year (if you can wait that long). Removing the lettering should be fairly easy. The street price on these cars should be in the $10 to $11 range since the four pack lists for $50.
In addition, once in a while you can catch a deal on the Atlas fishbelly side hoppers. There's a lot of seven Western Maryland cars out there right now, for example. You'd have to repaint since they're oxide red and the O&W cars were black.
There is a comparatively large amount of lettering on the GN car which will take some work. I wouldn't sand, by the way. There is a product called "Easy Lift Off" which has worked pretty well for me with MTL cars (and great with the newer Atlas cars as well). It's made by Polly S (actually RPM). An 8 fluid ounce container of the stuff cost me $6.25 and it's lasted me two years so far.