I had a newer jumbo joe (2015?) so ymmv... but I never had a problem getting that thing PLENTY hot, especially considering that the standard weber charcoal baskets fit with only a couple of mm gap to the grate, so a full basket means your food is almost sitting on the coals. That always worked great for me.
As far as size... I have always read that the cooking grate was the same size, and have seen people referencing using the standard 18.5 grate to get the flip up sides or using the craycort. I have seen mentioned that there is enough variance that occasionally the grate wont fit but no first hand knowledge on either of these points.