Same at ACE Hardware for tapered rubber stoppers. In helping a friend with his Lund, we plugged the live well holes with the same plug as the hull plug, Walmart.
That’s what I used also, I found stainless steel ones.
you might be ahead to look in there and measure the hole you are putting them in.
I got the tee handle style so that I could tighten them after they were installed.. only way I get water in now is when it comes thru the lid..
I also unhook hose from the live well pump so if someone turned on the pump no water goes to it…
I use my front live-well for pretty close to dry storage.
Water can get in past the lid….
should add I tried corks first, they did not work for me..
maybe if put from outside but did not for me on inside…