Grady White Sleeper seat convert to Pedestal?

I'd venture a guess that they don't drill a hole if they don't have to. But you should be able to look under the slider and see whether or not it's there. You didn't mention what model you have, but open the slider and check.

Either way, it's sort of a moot point - you need a hole if you want to use a split ring backer plate along with the Togglers. Ideally, a backer is preferred to spread the load better. Holes are easy to drill

You might try getting a hold of GW and ask about placement for the pedestal to make sure you don't accidentally drill in the wrong place and run into something below (stringer. etc) and then have to drill again.

This is my 215 I ordered from the factory with two deluxe helm seats, one replacing the lounge. I’ve since sold the boat but one buyer wanted to convert it back to a lounge so we looked briefly at how seats were mounted. I would call Grady to confirm, but I think the pedestal base is surface mounted using 6 decent size Phillips head screws. I didn’t remove a screw to double check the type as the next buyer liked the configuration and didn’t plan to change the seating, ultimately purchasing the boat.

Yes, normal practice for B-2-B seats is to simply screw them into the deck. They don't require the thru-bolting that pedestal seats do because of leverage/small base. I've seen some boats where only two of the fasteners used are thru-bolts and the others are screws... but in my opinion, it's best to thru-bolt all of them... especially since it's about the same amount of work.