I have always heard it was for the crank harmonics. I've not heard about the a/f bit but that sounds very possible however on many engines witha signle plane, especially race (single plane) stuff, the varience in outboard cylinders is very small. Under a couple inches in port length anyway. I know it helps get rid of the crank stress at high rpm. But it'snothing I'd ever really consider. I also believe some opf the fastest FAST cars use that swap. They have to use factory dual plane manifolds so the mixture deal makes more sense.