Doing a bit of precise measuring, it runs out at a height difference of about 5 and 3/8th inches, the height of a corner piece of Steck, and this may be too fiddly, although a bit of packing might solve any minor differences in height. It would allow Steck piers for supporting the bridge. It would be a single span bridge if there were two lines along the back as I only have two bridge lengths. If it were a single track along [part] of the back, then it could be a double span bridge.
I'm fairly confident that the trains will run OK without derailing or other problems. If we went the whole hog as regards length and width, would it be possible to have display, say, two and a half feet clear of the wall to allow access to the rear?