Well, yes. You're right. Stockton and Connor were the pair with three stacks.
But the term "flush decker" doesn't really fit as a distinction here, because all of the Caldwell, Clemson and Wickes classes were classic "flush deckers", in that they did not have a raised fo'c'sle like other destroyers of their day. Indeed, Caldwell was built with four stacks. The Caldwell class of six were experimental, built to various combinations of details - a modeler's paradise!
Besides having three stacks, Stockton and Connor had a different engine arrangement, three screws (the only in the class) and a different hull form aft, that was shared by all of the Caldwell class. (this stern shape is best shown by the photo on the Navsource page for USS Manley DD-74, second photo down from the top) DD-71 Gwin also had three stacks, but only two screws, and the standard turbine arrangement. Gwin was scrapped before the Lend Lease became a glimmer in FDR's eye. Stockton was one of the ships with a twin 4"gun mount on the fo'c'sle, but the other twin 4" gun ships and 5" gun ships came from the Clemson class.
Bottom line: we gave Great Britain 50 flush deck destroyers, but two had three stacks and three screws. These, as you say, were Conner and Stockton.
Your turn.
Rick