I can't show you a demonstration to prove that they're not interchangeable, but I'd bet my left arm that they're not.
Honestly, I have a pizza stone that would fit on my 26" no problem, and I could find a griddle that would fit without a lot of difficulty... my wok won't fit under the lid, but that's only because it has a long handle on one side - one with two loop handles would fit easily. I've pined over the GBS accessories, but having this much space kind of makes them redundant.