I don't have this lens and can't find a good photo of it, so my advice is just from other lenses I've seen. The usual construction would have 3 screws, not 2. That might be why the ring is loose. The screws don't go into specific contact points, but usually the aluminum underneath is dimpled a bit from previous contact. You're right about alignment. The ring is normally trapped between the focus and aperture rings, so it won't fall off even with no screws, but it will be annoying flopping around. An eyeglass repair kit might have screws that are somewhat close to the right size.
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