With a high volume one-piece toilet, you won't want the Flood Safe supply.
I would remove the existing supply tube with the lower nut and match it up at a hardware store.
It's a little hard to tell from the drawing, but it looks to be either a 3/8" comp or a 1/2" comp. On the West Coast, we use a 1/2" from the wall with a 3/8" supply line. but I know that the East Coast likes 3/8".
You can also use rigid pipe there if you feel handy.