No one makes a drop down , you have to make it . Either start with a factory original and cut the carb horn and weld it back together or get the fiberglass one that member Paint it Black sells and modify it grafting in the base of a 14" drop base unit.

There is another thread I think in the resto forum where Jim Lusk showed a picture of an original he modified .

As long as you get it down low enough it will work with the duct work , I'll be doing one if I end up putting a wedge back into my 69 bee instead of the Hemi.