Sabre, Custom II, Custom III, etc.
On the right end of the carriage, in front of the rails, there are two screws. The outer screw is for lowercase, and the inner screw is for uppercase. The left side of the carriage has only the lowercase screw for some reason. You may need to adjust both for lowercase tuning.
Royal 1970s Shift
It seems common with these machines, that one or more typebars toward the edges will strike the top lid/cover. Try tapping the rear edge of the lid with a hammer, toward the front of the machine. If that doesn’t solve it, remove the lid and flex it slightly, bending the left and right sides downward. Replace the lid and try the problem keys again. This has fixed every machine I’ve had a clearance problem with.