Do you really mean setscrews, in that the quadrant is threaded and the friction of the setscrew against the stock holds it in place? Or do you mean a retaining bolt, in that the quadrant has a hole in it in which a bolt passes through the quadrant and the threads are in the stock?
Setscrews that provide a friction grip have a place in this scenario but used alone they can work loose and the quadrant will spin on the stock just when you are trying to get into that tight slip and the whole world is watching.
To keep the wheel
aligned with the rudder
depends on the quadrant not moving on the stock. When the quadrant is exactly where you want it, you need to tighten the setscrews, then mark and drill the quadrant and the rudderstock. Drill through the quadrant in to the rudderstock and tap the hole in the stock. I have drilled through the stock and through bolted also if this is simpler to do. Drill one side of the quadrant to a body clearance size for the bolt and thread the other side. Or just drill completely through and put a nut and lock washer on the other side. It is not easy to drill it in place and get everything really spot on with a hand drill but you can get close enough for a through bolt. On this size stock I would use a ¼ inch or 5/16 bolt.
One or two setscrews and one through bolt and it won’t go anywhere, it won’t hurt the rudderstock and it gives you an alignment point when you pull the rudder
the next time.