Are they the slightly more angular cuts we're used to seeing there in OZ?
Maybe two kettles, but depending on wrapping & glazing, which you've already got good guidance on above, maybe even three.....I like to keep things flat......rib racks work but are kinda hard when there's liquids in foil, etc.
If they're big, two per :
if they're cut smaller width, three or even four with racks :
(I've seen a guy do 9 of these on a WSM, but the coals are not right close like a kettle)
the smaller width, 4 to 4-1/2 hrs.........big ones up to 5-1/2 hours + like Troy says....at about 250~265F
Bend test for doneness :
What are they cut like & what kind of setup are you comfortable with?..... helps us help you !!
G$ is right on, too.....run clean & do as little fiddling as possible......