The first thing I did was carefully joint the two pieces of the top face to face. By the way, that's Maude in the picture below, with her painted knob and tote and bakelite adjuster carefully stowed away in a drawer, replaced by rosewood, brass and a Hock blade and chipbreaker. As usual, Maude worked great.
Then I installed the hardware, two latches on the sides that pull the pieces together and two positioners (I don't know what else to call them) in the middle that fix the position of the "leaves" side to side and up and down.
I don't like this, but it was the best way I could think of to do what he wants. Another way that occurred to me as I was doing it is to glue blocks onto the bottoms of the pieces at the joint line and fasten them together with bolts. It would have taken longer to take the top apart but would perhaps have been a little more secure. Oh well.
The remaining task is to come up with a way to fasten the gallery to the rear stretcher that will allow it to be removed quickly. He will need to be able to undo the latches and slide the gallery back in order to disengage the positioners before lifting the gallery up. That means the attachments in the back will have to accommodate a considerable amount of movement. I've got a strange idea that I think will work.