"...the No 1 siding at 548 ft and the No 2 spur at xxx? ft (can't read the numbers) make sense, but what is the other No 1 at 352 ft? Is that the bridge / trestle length?..."
-The no. 2 spur is 273 ft. Every station seems to have a spur or siding no. 1, so these numbers apparently only refer to which siding or spur at a given location.
-I think the other no. 1 is the back of the wye. The 352 seems about right for the lenght (in feet) of the track that connects the Black Hawk and Silver Plume tracks (this piece isn't shown on the profile, curvature, or rail charts as it isn't part of either branch).
The bridge number (28.43) is the milepost location. This could get confusing as milepost numbers continue on both branches, so bridge numbers on the Black Hawk branch are intermixed with those on the Silver Plume line.