The stresses on the transom would be minimal as all the thrust force generated by the jet are transmitted to the hull through the intake bonded to the keel. Any loading from the engine will also be transmitted into the hull through the intake via the epoxy.
With that being said, I did notice a significant amount of movement at the stringer mounts of my blown/injected deal, but that was also with full stringers and full floor.
If you are noticing any kind of movement now you might ensure that your stringers are indeed sound. A rail kit won't fix a loose stringer.
Good luck,
Joe
