I don't have any documentation / plans since I made it up as I went along. I can post some more pictures and some measurements.

As far as stability, I can put my shoulder into it and push hard in any direction and it feels real solid. That said, the lumber does have a little spring to it. If I push/pull rapidly parallel to the body length, I can get the whole thing to oscillate a bit. There is no creaking or scary noises, and it stops shaking as soon as I stop.