I cook chuck rolls a lot, my Sam's carries them for restaurants who grind their own hamburger so you have to ask for them. Since they are boneless, they are simple to break down should you choose to. I like them closer to 16# so I can get one nice chuck roast and grind the rest.
I agree with injecting, and keeping the seasoning simple when cooking. I would suggest using a finishing rub when you shred or chop the meat, and make a lower salt version of your injection (or a nice au jus) for keeping the meat moist, or for dunking like a French dip. Those little styro cups that they sell night crawlers in are great for dipping jus.
Cooking the whole chuck roll is totally doable, but I don't think I've ever cooked a chuckie that was not wrapped or that was panned and wrapped, or that was not finished in a 18qt roaster. Chucks just benefit from a wrapped step. I would have some HD foil handy just in case.
There is no time to practice the 'roaster finish' method for an event this important...., but it's awesome for a buffet like situation for sandwiches. This works good with butts too. I generally smoke the meat all night and get it in the roaster by 9 or 10 am. The seasonings are dry French onion soup, dry Italian dressing mix, and a mild broth. Adding some mild pepperchini peppers is an option.
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