All I think he would really ‘need’ is an adjustable screw leveler-type arrangement on the ‘far’ side of the turnpiece: using the pivot as a fulcrum this would let him slightly raise and lower the track height at the gap when closed.
You’re right, though, that a better arrangement ought to be built, and that it should be ‘fine adjustable’ at or near both railheads … and perhaps at the hinges on the back side, too … to get the rails precisely level across both sides of the dropdown. We have had a number of threads on the ‘best practices’ making these, both as dropdowns/hinge-ups and physical takeouts.
My own thinking about what he is doing is to provide adjustable upside-down V guides that engage pins or mating plates on the open side of the bridge. As he raises it up, the Vs automatically align the outside end of the bridge; the bottoms (or interference fit) determine the final position, and he can then block or cam the securement to use mechanical advantage in locking or unlocking without having to fiddle with adjustment every time. I believe other posters have only used one, if the bridge has little tendency to warp; there might be an advantage in having two (one per rail) as any twist over time could be accommodated relative to the desideratum of keeping the railheads precisely aligned.
At the hinge side, I don’t think you don’t want the hinge to have to be the alignment long-term if you can avoid it. I’ve seen simple pins and sockets used to strengthen these joints; I think there have been some good suggestions on hinge-side alignment here over the years.
