Researching work benches will often show many examples of the sliding deadman. I opted not to put one on my bench because I valued drawer space more.
On the rare occasion when I need to support a piece from the bottom I’ll just use a clamp in expansion mode.
I use an inshave (aka scorp), compass plane, curved scrapers, and sandpaper for my seats. It’s laborious! Just started on another tonight and of course it has a few stubborn spots.
Good question about the bench. It’s a 5" pine top but it dried funny, curving inward at the top. So I inlaid a maple strip to get the front back to square.