I haven't investigated this option but as long as the dimensions will allow I don't see why it wouldn't work. Just need to be sure it will physically fit or you may have to make some adapters or supports but no biggie. I believe it comes with supports to span out to the main rails. Let us know if you try it.
Don’t know about the IW 650 but I just got the GMG pizza oven and it fits perfectly in the IW 885. Only had a week, one of boys cooked a couple pizzas. He put stuff on ‘em I won’t eat but they were a hit with his brothers and friends.