I'm kinda coming out of left field here, but instead of all this fancy crossover work.... wouldn't it be simpler, lighter, and easier just to run the pipes together with a Y and run a single from there back and accomplish the same thing?
The pipe would have to be HUGE. a single pipe would have to be 4.25" to have the same cross sectional area as dual 3". Hard to tuck that under the car. It likely doesn't have quite the same scavenging effect either.