Jim, on the 4x5 field camera I made the racks were small and I was not sure that cementing them into slots, no matter how tight, would work. I ended up brazing on brass extensions to the bottom of each rack and drilled holes for screws. the racks were screwed to the extension frame on the inside. I have two racks sitting here for the 5x7 I hope to build this Summer and I was thinking of either screwing them from the bottom up, drilled and tapped or from the top at each end with a pin or even a small screw.
I just looked to see how the Shen Hao cameras racks were attached and am surprised to see that they are screwed to the inside of the rail just like I did on mine. I had nothing to go on when I built it in the '80's, I guess mechanical attachments are intuitive.
I think if you were to put the rack in a tight slot with some cement/adhesive on the bottom and put a screw or pin at each end it will stay in place. You could of course cross pin it. Drill a small hole in the rack from the side and put a pin in from the inside or outside of the wood rail. It would hold it from forward and upward migration. One on each end and one at the middle would work fine. By pin I mean a small brass wire, you could plug the small holes with a sliver of wood and it would be invisible to the eye.
Curt