We obtained this sofa and were after any information about which company may have constructed it. It is Mid Century, probably reupholstered at least once, but is built like a tank.
It is very heavy, and I have shown photos showing beneath the seat with springs, string holding the springs in place plus two extra beams running back to front in addition to the edges which are about 3" solid wood, plus these metal, wavy supports which looks like paper but is actually steel. Then it has re-enforcement bars running all around the inside. Seems like it is over-engineered for a sofa.
The back cushions look like they do not belong - perhaps they were added when it was reupholstered?
I thought perhaps these design features might be recognized by someone out there.
Measures 82" long, 27.5" tall, arm rests at 22", about 31-32" deep. Very square, the back does not slope.
Any pointers appreciated. 
Not an unusual foundation, I'd say:
Coil springs with a steel strap suspension. Makes sense that it would need at least one cross piece, to resist the tendency of the front and rear rails to move toward each other, under load -- making a bowl of the seat plane. Over time, the straps might stretch a bit; they could presumably be tightened -- or the cross-pieces could be lengthened ? That's if it seems to be sagging.
I don't see the back cushions as optional, or additions to the original design . . .
Could be
I have heard of Dunbar's construction on their sofas, but I actually have not seen the inside of one. IDing sofas can be very hard with no tags.
We looked at so many on line and eventually it seems like most designers did a style like everyone else - it just seems that way.
After looking at so many on-line it seems like there are a few likely candidates, but it is really just guessing on our part.
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