Turns out my master bedroom 2 way register was installed upside down. It's very old, painted multiple times, so I bought a "1 way" (no grilles) thinking it would give me the strongest air flow, but the screw holes are 1/2 inch less so would need to drill into what I assume is the duct flashing, as was done previously.

This register is above my doorway, facing the bed. A 2 way register sends the air to a side wall and into a small dressing area hall. All things being equal, should I get a new clean 2 way (same screw holes) or use the "1 way". What I care most about in southern California is hot nights when the air may run during the night. I want maximum comfort for sleeping. I also have a ceiling fan that I usually turn on low whether or not air conditioning might be running.

Thanks so much. It's hard to decide what would do the best job.