Trainz

Okay so I'm working on doing a 3d model of a Ohio class locomotive (Lima's 4-8-6 superpower locomotive) and I'm working off of some plans I found on Google images and one of the thing i was wondering about was what Scale are locomotive drawings done in generally since I would like to at least trace out the basic shape of the locomotive since there aren't really any locomotives of this type that ever existed.
If you guys can help that would be great.
Martin.
P.S. also suggestions to where I could find any more detailed drawings would be great as some of the dimensions are a bit hard to read on the one i currently have.