The gun carriage itself is slightly elevated and there's iron bumpers at the rear of the track to slow and ultimately stop the recoil of the massive gun. The actual rolling carriage has a wooden beam which reaches between the tracks of the lower carriage which is designed to slide right into a quite substantial cross beam to also dampen the impact of the recoil on the iron bumpers. As for the sights, they'd usually be stored separately from the gun, only brought up to fire. This was to prevent the fairly complicated sighting mechanism from being damaged in weather or enemy bombardment. Common practice for gun crews of these guns was to hide safely in their bombproofs during bombardment, periodically emerging to fire their gun. The crews would mount the sights when firing, and take the sights with them when retreating to their bombproofs.
Great job. The figure really adds to it.
There is a Columbiad at Columbus-Belmont State Park that was dug up out of 30 feet of Mississippi River mud. It has a wheel to move it back into firing position.
That would be neat to have in my office but I got too many cannons now.