A piece of stiffly moulded, curved auto heater hose would make a neat intake manifold extension, making either of those frames usable. Most of the motorcycles I have owned, including my BMW R75/6, have a section of rubber tube connecting the carb to the intake manifold runner. In the case of these frames, a little 90 degree bend of rubber hose would hang the carb off to one side and also allow it to be vertical to ensure the float works right.