It’s hard for me to tell from the pictures but I usually just use simple tabs.
Sometimes it’s a bitch to get to all four of the seat bolts so it helps to make sure you have enough room to fit your hands in there and tools.
2400 lbs before you hit yield from bearing stress. I'm not sure what reduction factor you would get from the hole expanding but you can go far beyond yield for this bearing stress before you get failure. I think it's safe to say the nut is good for 2400 +/- 1000.