The parts that are not interchangeable include: cookbox, bottom pan, flavorizer bars, burners, manifold, control panel. The frames are different to the point you cannot stuff a 1000 cookbox into a Silver B frame. I was advised it would not work and the advice I was given was correct, though I tried anyway.
Parts that will work on both the silver B and the 1000 are: Lid, cooking grates, and I think you can make the igniter work.
You can fit the Silver B table ends, and trays, but the 1000 frame doesn't have a catch for the swing up table to stay up.