competition shoulder? Would this be for an MBN/MiM competition? If so, you're going to want to have 1 whole shoulder for each of the 3 on-site judges, 2 for your blind turn-in, 2 for finals (fingers crossed that you make this), and probably a couple as the ones that dont make it to "prime time". 7 MINIMUM, 8 is probably best, 9 of you can fit 'em.
How to prep them? Exactly like you would a 9# butt, and if you have good air-flow in your smoker the 20# whole shoulder will cook in pretty much the same time as a very large butt.
MBN/MiM really leans towards pulled pork; not chopped or sliced. If you can get a Money Muscle or two for blind, good deal, but honestly it's going to be tough to get the MM sliceable and perfectly tender without being mushy and still have enough pulled pork perfectly tender. Might put 1 or 2 (if doing 9) on an hour or so later than the others, or pull them off early. Anyway, fill the box with pulled pork (not shredded), mixing in some bark.
It's done when it's done, but usually it's 195-205 temp. Money muscle is under 195, more like 185.
Hance - Lake Dogs Cooking Team - MiM/MBN/GBA CBJ and comp cook
Lake Sinclair, GA (strategically about an hour from everywhere)