In the past I’ve used item pipes and filters to sort the dusts out into different hoppers feeding different dust funnels. I realized you can do this with a single hopper coming out of the roaster set to output exact stacks of 36 ( when the recipe outputs 72nds of dust, like galena ), and have the hopper insert into a single dust funnel to the side ( so the funnel does not pull from the hopper above ). The hopper will buffer some of the output of the roaster for a while if the dust funnel is “stuck” with half a unit of dust, but as soon as the next half unit drops, it will clear the funnel, then the other metal dust holding in the hopper will drop. Thus the dust funnel switches back and forth between lead and silver with no need for filters or pipes.
I just use barrels, they already convert any dust size to the one you initially put into the barrel.