Mark,
I'm posting the latest designs we've come up with substituting Ross switches for the GarGraves switches in the original versions. The version in this first photo uses standard switches. As you can see, in order to accommodate the engine spurs, the loop now covers some tracks below requiring a tunnel or some unique way to deal with the overhang. The Red circles denote tracks that have to be cut. The curvy tracks with no color show how the hidden spur would run if you substituted an O42 switch for the Wye switch.
The version in this second photo shows the same basic design with 2 modifications. The curve in the upper left now uses a Ross Curved O72/O54 switch. As you can see, the loop needed to be move more to the right and doesn't cover as much track below. However, in order to accommodate the engine spurs, I had to keep the 2 GarGraves O42 switches in that area.
Because there was some concern about reach, I added 30" circles to show how much of the track runs could feasibly be reached from the edge of the bench work and the access hatches. As you can see, there is one section along the top right where a stool will need to be used. There is room for an access hatch, but it would be to be a little less than 18"x24".
NOTE: In both versions, the grade starts just inside the tunnel. If you start the grade outside the tunnel, the slope increases from 3.0% up to 3.4% depending on where you start it. I relocated and reoriented both spurs inside the loops to give you as much space as possible for landscaping. The centers of the tracks along the walls are on the 5" grid mark and should allow clearance for the engines and rolling stock you intended to run.
NOTE 2: The only other thing I can think of to try is to move the lower section of grade track closer to the wall and extend the tunnel. I don't know if tunnels on inclines is prototypical, but it would allow you to landscape that entire area as the side of a canyon and it would look like this:
