I might be out to lunch here, and this is untested, but I have an idea. I tried something similar to this recently with some difficult arrowroot paper and it worked pretty well. I'm not sure what you're planning to coat John... paper should work but I think the salted gelatin might be difficult to get to stick to glass.
If you coat salted gelatin, let it dry, and then coat silver nitrate on paper, it will probably be like a salt print ( which often has a little gelatin in the salting solution ) and have a very limited shelf life. I usually figure no more than about 12 or 14 hours.
With my difficult arrowroot paper, it had already been coated with salted arrowroot and dried, then I coated the 12% silver nitrate, let it sit for about 1/2 hour, and washed it well in several changes of DH2O.
What I did then was let it dry for about 6 hours and then coat with 2% AgNO3, let it dry again for 3 hours, and print. I wondered at the time if the dried "silver chloride paper" might keep.
I think the washing step will remove all the excess silver nitrate and any excess salt, so my hunch is that it might keep pretty well and have only silver chloride left. In your case the silver chloride ( or bromide, or whatever you are using ) would be in the gelatin. Since you're going to develop it, you wouldn't use that last 2% silver nitrate step that I needed for printing out, but just expose it.