Well, one dualist set has two fighters, the other a fighter and Felix. So a combo of an LVG, and camel would work, or a variation of the other two place singles: DFW, Rumpler, Hannover, or a W-12 variant. A Camel and DVIII would introduce two new kits. The Triplane/ Camel would do the same.
Add to the equation that the Felix was a new kit, and the W-29 OOP, and the LVG/Camel boxing is more of a possibility. How about a Camel/Gotha?