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You'll want to make sure that if you do cut them in half, the side with the smaller amount of meat/fat should be kept on the top rack, the thicker half should be on the bottom rack. The thinner half may be ready to pull from the smoker a tad earlier than the more meatier half.
I think the only time I've never cut them was when I smoked them on my grill. Now I have the rib rack kurtsara sent to me so I can stand a bunch of them in one spot but they'll still have to be cut to fit in the ECB or the RO. They'll cook up just fine as long as you follow the good advice of thinner/smaller higher.
If you buy a MES 40" no need to cut rib racks. 4 shelves 4 per shelf (using standing racks) or 16 wonderful racks of ribs. I have done up to 12 racks of ribs, not bad for really a fairly small footprint smoker.
I can weasle a slab of ribs on my WSM, but I've been finding that the ends typically are more done...dare I say a tad burnt? I'm assuming this is due to the heat rising along the circumference of the smoker - around the water pan. Next time I'm going to cut in half.