Digging a bit deeper into the McCloud River web resources it does seem train lengths for the most part were fairly short and operating speeds low. I'm not sure how that would translate into a driving experience in a train sim, as going at 15 MPH for 12 miles through dense forest is going to get a bit tedious. I suspect some compromise would be needed in that area.
I scrapped my first attempt at the route as I couldn't get the Libre maps to line up quite right in Transdem and there's not enough detail on the Google/Yahoo maps that also come out very blurred on the terrain. However looking on another thread I think the Transdem author has sorted the issue with MS changing the Terraserver, which will allow US topo maps to be overlaid along the route. At the moment I must confess to starting the route off in Railworks

:n: (purely as an exercise) but a Trainz version is still on the cards. I've also managed to make contact with someone who is looking to see if they can resource the gradient profile and detailed trackplan.