Selig lounge chair question  

A picture is worth a thousand words
Here is a photo of it.. 🙂

no
The space between the seat and the back should be open--no brackets or anything else. The thick metal plates on the sides are what hold it together, as you guessed.

Sorry Spanky
But this bracket is supposed to be there. On all of the chairs I have seen there is the metal bracket- complete with hardware that matched the rest of the chair. When I was redoing my plycraft I tried to leave the bracket out - even gently sitting on the chair resulted in cracking sounds so I quickly put it back in.

Interesting!
My Selig chair doesn't have a bracket and never had one. But the Plycraft chair that I haven't redone yet does have a bracket, as does one of the chairs that I redid that's gone now (I checked photos).
Odd how the brain remembers things. Or my brain, anyway.

The second
The second chair I redid was a Selig and the backrest had broken away from the frame like in Rocklands picture. I remembered because it was a bear trying to bend a steel bracket into the correct shape to replace it.

I'll post pictures in a...
I'll post pictures in a little while.
What I ended up doing is this:
Where the steel bracket attached to the seat base it had ripped out some of the wood. I cut out a large area of the plywood and replaced it with slightly thicker new plywood, and then I sealed it all with fiberglass, and went ahead and fiberglassed the entire top part of the seat base, including the area where the arm rests attach and the little rhomboid metal bracket attach. It's not pretty, but you'll never see it under the cushions, and now the entire bottom of the chair is *sturdy*. Also on the bottom part of the seat base I attached an extra piece of 1/2" plywood that is larger than the area the stand attaches to. This gives over 1" of material (plywood + fiberglass) that the stand attaches to and that the back bracket will attach to. So it is strong.
On the lumbar seat base I also fiberglassed where the back bracket attaches and also where the rhomboid brackets attach. I sat in the chair with only the rhomboid brackets and not the back bracket, and it felt ok. But I didn't want to risk things, so I bent the bracket back into shape and reattached it to the chair.
I really feel the fiberglass has helped reinforce the strength of the plywood. It was old plywood.
I then sanded everything and restained the entire chair walnut and then sealed it twice with a semi-gloss polyurethane. The grain on the chair is fantastic.
More info and questions when I post pictures in a second.

It's amazing
It's amazing what you find under that horrible 70s amber polyurethane crap they used. The grain on both of mine was incredible!