New to Factorio ... totally love it.
However, I've run into a problem that i thought i'd ask around if someone can help me solve.
I have a two lane output from my furnace's for copper and iron that ...

... i want to balance both lanes from over two mixed lanes on each side of my assembling machines for (as of now) science packs ...

... however i fail, no matter what nifty balancing setup i find online i cannot get it to alternate the sides of a two lane input.
I want to draw 1 copper from left lane then 1 copper from the right lane ... aso.
(Yes, i know im outputting over the current need of the factory)