There is at least one grade, besides Mason and Curry, that I know of on the South side of the mainline. It crosses Huckleberry Loop just inside the National Forest Boundary, and is noticeable by a through fill on the right side of the road. I attempted to follow it, but the land there is flat as a table top and I lost it in a maze of wheeltracks. It's connection with the mainline has disappeared in the dredge tailings.
I once went with Lyle Defreese to the upper edge of his ranch, and on the way we crossed several old grades. Lyle is friendly to the railroad and would probibly not object to some exploration. Same for neighbor Dan Warnock.