Been there, done that. In 1982 we drove from Mack to Watson, up to Dragon and Rainbow.
Moro Castle is amazing, it is like an Oregon logging road. If you walk it and then stand at the top you can almost hear the locomotives pounding around the curve. Difficult to believe they could get around the curve. If you get a chance go there. Walk up to the end of wye at Atchee and look up at the big slide.