Again, I give all the credit to "ShieldArc". He taught me how to design the fold down/latch up system. My first attempt wouldn't fold at all. Excuse my non-mathematical verbiage. The distance from the hinge pin to the table top pin must EXACTLY match the distance from the hinge pin to the lower leg pin. After that it's all secondary. Since I don't beat on stuff or load the extension with extreme weight I didn't worry so much about the supports. They are 1/4x2 flatbar that I had onhand.
Not sure these pics will help you, but it's all I got. Sorry to the OP for the distraction!!!!!
The OP doesn't mind. He likes to see what others have done.