I don't know it is too late, but I would trim the fat off of the top only to give more contact area for the rub and to get a nice bark in that area.
The last chuck short ribs that I did took just over 5 hours at 250, no foil. Cook them until they are tender when you probe them.
"Ron Rico, Boss. You can call me Captain Ron..."
The Naked Fatty!
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Remembering a friend