If we've been able to replace the default trains in msts could we super-modify the default Marias Pass to be as realistic as possible?

Its possible to do but all interactives need to be removed first then one can start from Shelby working west correcting trk,swt's,grades,trk curvature..ah heck just build a new route.

Have you seen Marias Pass 3.1?

Derek

Atrak,
although installation is rather complicated the GN-HiLine v3.4 is one of the best routes (freeware) available.
You must start with v3.0 then update that to v3.1, then v3.2, followed by v3.3 and finally 3.4. There are many posts on the TrainSim forums on how to successfully install the route. The install instruction will lead you but following them precisely is essential. And the various updates each have there own quirks so reading the first install and winging it will bring you to grief. Test each install before proceeding on to the next.