Hey, Brian. I inherited a drawing table that looks a lot like yours. Has the same base, but no criss-cross supports. Instead, has a straight bar across. The board has two metal arcs to adjust the tilt; they look like they should work with a crank or locking mechanism on the supports, but those pieces are missing.
They guy who had the board jerry-rigged it to work. I'm wondering if we have the same board?