AFB idle mixture screws

Looking for a replacement idle mixture screw for an AFB from a 68 Hemi. Carb # is 4431S It has a taper or step to it, and I do have a parts AFB that has a very similar screw, but its threaded at the step and will not fit into the carb correctly. The screw I need is on the top and the parts carb screw is on the bottom. Anyone have a used parts source?? or ideas.??