The b-35 had the props mounted on shafts that exited the top surface of the airfoil. The shafts had fairings on them that acted as vertical fins. It wasn't the propellers that provided the stability. With the B-49 and its jet engines, it was found to need some vertical fins to restore the lost area of the fairings.

forgotenplane17: yes you can design an RC plane without a vert stab. Swept flying wing with dihedral. Use washout at tips for pitch stability. Use up-moving ailerons only, or spoilers for roll and tip-mounted elevators for pitch. I'd build it as a sailplane first, then maybe as electric. Balance would be pretty critical. Glo power migh not be so good: Having a fuel tank would make the CG shift around probably enough to make you unhappy. It would fly with a symmetrical airfoil. It would be more efficient with a reflexed airfoil.