I have not smoked a chuck roast this way, so I cant actually answer that. But, I will say your plan sounds great. The two pieces will cook as two pieces, unless you have them tied together really well, then they may take a little longer based on the total thickness. But, separately they will cook individually.
The chuck roast may not be very tender due to the type of cut it is. Perhaps it will be fine and others will comment. When I’ve served chuck roast as a roast, I’ve done Sous Vide at a temp of 131F for 30-48 hours, then chilled, then brought to The 131F temp on the Weber or Smokin-it. This provided great rib roast style tenderness.
But, I still think your plan will help with what you are after. Enjoy!