It's just the flat flares for the XJ. There is a slight gap in the rear for the MJ though.
As for the rest. I'd say it really boils down to what axle you're going to run. Personally, I'm not a fan of anything above a 33" on a D30, can you run 35's on it, absolutely. The issue becomes the cost to upgrade the D30 to effectively run 35's vs just going with a HPD44 or tons. Plus the geometry of a D30 sucks once you start getting, tall 5"+, you can do the WJ swap but it's not cheap. For my MJ I'm planning to run 33's with a decently built D30 (selectable locker, 4.56 and WJ swap) , my Xj will run a HPD44 and 9" for 35's. When I had my other XJ I had a D30 and 33's, with the exception of being on 4.11's it handled everything just fine. I found 33's a good overall size for what I was doing, mild wheeling and daily.