At that size I'd suggest cutting it in half for more surface area for smoke and rub and salt. Without splitting one that big you're likely to find it bland and lacking in smoke flavor and bark once it's all mixed up.
I've had great pulled beef results from 275F - 300F on the WSM, foil around 160F internal, finish in oven at 225F or higher until it's falling apart tender. Rest a bit then pull.
Try to reserve all the foil liquid if you can, if there is enough defat it and add it back in to the pulled beef.
At those temps I'd think 14 hours would be plenty for two 9lbers ... but I don't keep real close track of that stuff so it's just a guestimate.