To make sure I understand the joinery, set-ups, fixturing, and order of operations, I am building a version in inexpensive poplar before going further with the white oak.
A lesson learned: clamping across the diagonal may give the illusion that a racked frame is brought back to home. However, this position is not held once the clamps are removed. Instead, make subtle adjustments in the position of the pads of the clamps across the front of the frame, checking the diagonals with diagonal sticks.
This will have a happy life in my shop.