I just pulled my SnS out and dropped the 18" WSM ring into my 22" kettle, and it fits in there perfectly as a guide to keep a charcoal snake on the outer rim of the bowl. The cooking grate still rests on it's tabs, but there is zero room for a diffuser or water pan.
With that method, I could put a drip pan or water pan inside the ring, so that's cool, but it won't get me any kind of diffusion to shield the meat from direct heat from a snake.
Thanks for the links to those 3 options, that made it easy to compare the 3.
The new Weber thingy looks a little flimsy for the price, but it would have the added versatility of doubling as a vortex.
I was just hoping to slap something together with parts I have on hand, rather than buying (yet another) specialized gizmo for the ol' 22" kettle.
I just wish Weber would sell the ring from the Mastertouch diffuser on its own. It appears to just be the normal 18" WSM charcoal ring, cut in half so it sits lower under the cooking grate. That would be perfect with a 19"(?) Pizza pan on top as a diffuser/drip pan.
Oh well, I guess I could try levitating a pizza pan on a couple bricks or something, lol.
Thanks for the responses everyone!