E......it would most likely be better to have the wrapped ones lie flat if possible, elseways, the liquids in the packet will drop to one side.....kinda defeats the purpose of braizing the whole flat of meat that way...........
Depending on how big of a cut they are, you may be able to do one flat & one to try out the rack if you'd like.....these are fairly large full spares & they still have breathing room lying flat (coals are off to one side, not snaked all the way around).....
Don't know what style your rack is, but you might be able to set them perpendicular & have it work out......only time I use a rack is if I'm pressed for available lit kettle space (instead of starting another machine).......they're basically meant to increase capacity, not so much for any finished product benefit.............
This is the narrower St. Louis cut, two upright & the third flat across the top of two wires of the rack.....that may be a way you could set up?
......or......just use the multiple WSM racks......I'm a Kettlehead, so I always try to figure out how much I can get away with there 1st !!!!