Ted,
The D&S is running double headers Mon, Tue, Wed on the second train to Silverton leaving at 9am. They are coupling up the helper behind the Durango library. There is a bike walking ramp form the library down to the track. The ramp puts you right where the helper waits.
There are many places along 550 between there and Rockwood. Be careful when shooting as the traffic is heavy this time of the year with RVs and campers. A good spot is the Hermosa Meadows road (300 yards from my house). Long view looking down the valley of trains coming from Trimble Crossing.
A good spot is the hill overlooking the 550 crossing at Hermosa. Park by the crossing and walk up the hill, the folks who live there do not take kindly to people parking on the narrow road .
Shalona Lake Crossing is a favorite of mine. Have photographed there hundreds of times. It is isolated with no structures around. Only problem with Shalona is that it is so close to Rockwood that you cannot shoot the train in both places.
As was stated, the bridge south of Silverton is a great spot. The D&S calls it the "long bridge," It is a brisk walk from the spot where you can park. Don't forget you are at 9000 feet, but I can do it at 81.