I have cooked 4 racks of spares St Louis cut and 2 fatties as well as MOINKS on my 2 rack UDS. It all pretty much was a comfortable fit with a regular flat drum top. With the Weber lid as many use, you could get more on it I'm sure.
If I could I would. If I don't, it's because I am to lazy!
UDS | Brinkman Gasser | Big Poppa Drum
On Deck: Weber OTG