I took the first attached photo about a decade ago. Someone made this bracket to support their bikepacking type saddle bag.
George, that support in your first photo consists of the hoop connecting the two side plates of an original Blackburn Lowrider front rack. The connectors are sourced from an original (Mk1) Tubus Cargo rack (rods and adjustable tilt-plate, around 2007), a reflector bracke, and a piece of aluminum 90° angle. I found the same photo back in the day and made one using the same parts!
It worked well enough in concept and was stable, but the aluminum rod hoop was unnecessarily long and began to show signs of stress at the clamp. Also, it wasn't compatible with my rear pannier rack, so it didn't remain in service long. A good try, though, and top marks to the original innovator for repurposing existing parts!
The "handlebar bag" under-bag support on the seatpost is really clever, George.
When Forum member JulianK kindly gave me his old CCL, he included a Karrimor-style uplift bracket that engaged my Brooks saddle loops. It released quickly and easily, but I largely stopped using it out of concern larger loads could apply a lot of torque to the saddle loops, especially on bumpy roads. That started me noodling for something more solid, like the billet Q/R I described above. I really must spend some time out in my metal shop to bring it to reality!
I bought Thorn's extended T-bar uplift back in...2011, I think. It used machine screws and acorn nuts at either end of the cross and the idea was you could leve the CCL's leather straps a bit loose and so ease them over the acorn nuts when you need to quickly de/mount the bag. It worked but wasn't as stable as I'd hoped.
I also tried the nylon boat cleat trick...bolting the cleat through the bag and into the hardwood dowel. Undo the lower seatpost strap, give it a little wiggle, and the cleat's crossbar slipped between the saddle rails, yet was secure otherwise. Unfortunately, it tended to rattle unbearable on rougher roads and the bag wiggle a fair bit as the cleat's nylon crossbar wiggled back-and-forth despite the lower securement.
Best, Dan.